v2.2.0: Qualified references (#43)

Closes #39 by adding fully qualified names in the generated Elm code when referencing definitions from other modules.

* Adds 'module' to schema definitions,
* passes the schema definition context - instead of the type dictionary - to each printer function,
* uses fully qualified names when referencing types, encoders and decoders
  from other modules in the generated Elm code,
* removes the explicit import of types, decoders and encoders from other modules in the generated Elm code. Now just import the module and nothing else,
* adds support for the 'title' property in the schema root object,
* removes some code redundancy, and
* updates readme with new elm output.