redirect function docs to website

Author: andrew-coleman

functions.md

@@ -1,199 +1,4 @@
 ## JSONata Function Library
-The following is a proposed function library for use within JSONata expressions.
-This is work in progress. Some of these functions have been implemented, and those that have not are marked accordingly.
+The documentation for JSONata and its function library has now moved to http://docs.jsonata.org.
 
-
-### String functions
-#### `$string(arg)`
-
-Casts the `arg` parameter to a string using the following casting rules
-   - Strings are unchanged
-   - Functions are converted to an empty string
-   - Numeric infinity and NaN throw an error because they cannot be represented as a JSON number
-   - All other values are converted to a JSON string using the [JSON.stringify](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify) function
-   
-####`$length(str)`
-
-Returns the number of characters in the string `str`.  An error is thrown if `str` is not a string.
-   
-####`$substring(str, start[, length])`
-
-Returns a string containing the characters in the first parameter `str`
-starting at position `start` (zero-offset).  If `length` is specified, then
-the substring will contain maximum `length` characters.  If `start` is negative
-then it indicates the number of characters from the end of `str`.
-See [substr](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/substr) for full definition.
-
-####`$substringBefore(str, chars)`
-
-Returns the substring before the first occurrence of the character sequence `chars` in `str`.
-If `str` does not contain `chars`, then it returns `str`.
-
-####`$substringAfter(str, chars)`
-
-Returns the substring after the first occurrence of the character sequence `chars` in `str`.
-If `str` does not contain `chars`, then it returns `str`.
-
-
-#### `$uppercase(str)`
-
-Returns a string with all the characters of `str` converted to uppercase.
-
-
-#### `$lowercase(str)`
-
-Returns a string with all the characters of `str` converted to lowercase.
-
-
-#### `$split(str, separator, limit)`
-
-Splits the `str` parameter into an array of substrings.  It is an error if `str` is not a string.
-
-The optional `separator` parameter
-specifies the characters within the `str` about which it should be split. If `separator` is
-not specified, then the empty string is assumed, and `str` will be split into an array of single
-characters.  It is an error if `separator` is not a string.
-
-The optional `limit` parameter is a number that specifies the maximum number of substrings to 
-include in the resultant array.  Any additional substrings are discarded.  If `limit` is not 
-specified, then `str` is fully split with no limit to the size of the resultant array.
-It is an error if `limit` is not a non-negative number. 
- 
-#### `$join(array[, separator])`
-
-Joins an array of component strings into a single concatenated string with each component string
-separated by the optional `separator` parameter.
-
-It is an error if the input array contains an item which isn't a string.
-
-If `separator` is not specified, then it is assumed to be the empty string, i.e. no separator 
-between the component strings.  It is an error if `separator` is not a string.
-
-#### `$format(pattern, ...)` - to be implemented
-
-  [printf style formatting](https://en.wikipedia.org/wiki/Printf_format_string#Format_placeholder_specification). Other formatting schemes are available.
-
-### Numerical functions
-
-#### `$number(arg)`
-
-Casts the `arg` parameter to a number using the following casting rules
-   - Numbers are unchanged
-   - Strings that contain a sequence of characters that represent a legal JSON number are converted to that number
-   - All other values cause an error to be thrown.
-
-#### `$abs(number)` - to be implemented
-#### `$round(number)` - to be implemented
-
-Rounds up to the nearest integer
-
-#### `$roundHalfToEven(number)` - to be implemented
-
-  [Round half to even](https://en.wikipedia.org/wiki/Rounding#Round_half_to_even) Commonly used in financial calculations.
-
-#### `$power(base, exponent)` - to be implemented
-
-### Numeric aggregation functions
-
-#### `$sum(array)`
-
-Returns the arithmetic sum of an array of numbers. 
-It is an error if the input array contains an item which isn't a number.
-
-#### `$max(array)`
-
-Returns the maximum number in an array of numbers. 
-It is an error if the input array contains an item which isn't a number.
-
-#### `$min(array)`
-
-Returns the minimum number in an array of numbers. 
-It is an error if the input array contains an item which isn't a number.
-
-#### `$average(array)`
-
-Returns the mean value of an array of numbers. 
-It is an error if the input array contains an item which isn't a number.
-
-### Boolean functions
-
-#### `$boolean(arg)`
-
-Casts the argument to a Boolean using the following rules:
-  
-| Argument type | Result |
-| ------------- | ------ |
-| Boolean | unchanged |
-| string: empty | `false`|
-| string: non-empty | `true` |
-| number: 0 | `false`|
-| number: non-zero | `true` |
-| null | `false`|
-| array: empty | `false` |
-| array: contains a member that casts to `true` |  `true` |
-| array: all members cast to `false` |  `false` |
-| object: empty | `false` |
-| object: non-empty | `true` |
-| function | `false` |
-
-
-#### `$not(arg)`
-
-Returns Boolean NOT on the argument.  `arg` is first cast to a boolean
-  
-#### `$exists(arg)`
-
-Returns Boolean `true` if the arg expression evaluates to a value, or 
-`false` if the expression does not match anything (e.g. a path to a non-existent 
-field reference).
-
-### Date/Time functions
-tbd
-
-### Array functions
-
-#### `$count(array)`
-
-Returns the number of items in the array
-  
-#### `$append(array, array)`
-
-Appends two arrays
-  
-#### `$flatten(array)` - to be implemented
-
-Flattens nested array into flat array
-  
-#### `$range(start, end, increment)` - to be implemented
-
-Generates an array of numbers starting with `start`, not exceeding `end`, in increments of `increment` (defaults to 1)
-
-### Object functions
-
-#### `$keys(object)`
-
-Returns an array containing the keys in the object.  If the argument is an array of objects,
-then the array returned contains a de-duplicated list of all the keys in all of the objects.
-
-#### `$lookup(object, key)`
-
-Returns the value associated with `key` in `object`. If the first argument is an array of objects,
-then all of the objects in the array are searched, and the values associated with all occurrences 
-of `key` are returned.
-  
-#### `$merge(object, object)` - to be implemented
-  
-Returns an object containing the union of the two `object` parameters.  If an entry in the second object 
-has the same key as an entry in the first, then the value will be overridden by the second.
-
-#### `$spread(object)`
-
-Splits an `object` containing key/value pairs into an array of objects, each of which has a single
-key/value pair from the input `object`.  If the parameter is an array of objects, then the resultant 
-array contains an object for every key/value pair in every object in the supplied array.
-  
-### Higher-order functions
-
-#### `$map`
-
-#### `$reduce`
+The docs are open-source on GitHub Pages: https://github.com/jsonata-js/jsonata-js.github.io