v2.3.0: Elm-style errors and Tuple types

Adds Elm-style error reporting and adds a TupleType.

• Streamlines error handling across all files using ParserResult and PrinterResult types, which encapsulate the result of parsing/printing a schema and any warnings/errors encountered along the way,
• adds parser and printer error util modules for pretty printing errors,
• moves the logic from Predicates.ex into their respective parser files,
• moves schema version logic into its own module, and
• splits most of parser.ex into root parser and parser util.
• Adds support for parsing tuple types (see http://json-schema.org/latest/json-schema-validation.html#rfc.section.6.9).
• Fixes a bug where TypePaths were missing 'properties', 'anyOf', 'items', etc. values.