Closes #671

* Add version badges

* Add Python 3.6 requirement

It seems as if the theme parameter was not passed in. As a result, the `index.html` does not change along with the JS/CSS resources that are made at the bottom of this particular routine. Not sure if there are other issues in this function, but this fixed theming for me.

* Initial pass at pulling in 'typesystem'

* Switch OpenAPI validation to 'typesystem'

* Use 'typesystem' for Swagger validation

* Drop validators/types, and use 'typesystem' instead

* Drop redundant dict_type

* Drop unneccessary checks

* Allow or disallow empty strings in various schema properties

* Use typesystem for validation

* Drop tokenization, in favor of 'typesystem'

* Switch to using 'typesystem' for validation

* Update requirements

* Don't return 'Document' instances except for OpenAPI/Swagger

* Blackify

* Add black to requirements

* Upgrade requirements

* Ues xenial distribution

* Remove server implementation

* Drop redundant URLEncoded and MultiPart codecs

* Drop unused exceptions

* Cleaning up tokenization

* CLI only

* Fixing up 'apistar docs'/'apistar validate'

* Drop commented-out Interact button

* Add 'apistar docs --verbose', and overwriting previous builds.

* Cleaning up 'apistar' docs theme

* Cleaning up 'apistar' docs theme

* Add redoc and swaggerui themes

* Fix for displaying validation errors in verbose mode

* Fix link to schema_url for swaggerui theme.

* Add schema test cases

* Improve Parameter validation for Swagger

* Update requirements

* Update setup.py

* Adding tests for Client(...)

* Exit with error on invalid schemas

* Add tests for cli

* Fixes for Swagger schemas

* Add 'apistar request'

* Add test case for petstore.swagger.io

* Linting fixes

* Update requirements

* Add support for apistar.yml

* Linting

* Drop redundant default=None on click options

* Rewriting docs

* Refactoring 'codecs' package into client/decoders.py

* Reorganizing layout

* Updating docs for new layout

* Linting

* Cleaning up

* Linting

* Add apistar.parse()

* Remove unused imports

* Finesse DownloadDecoder

* Drop unused import

* Documentation work

* Refine API

* Linting

* Drop trailing comma

* Sort imports

* Improve decoder interface

* Cleaning up

* Infer JSON/YAML encoding automatically, if not set.

* Add 'encoders' to Client

* Add theme licenses

* Cleanups

* Cleanups

* Refinements to Client library and updates to documentation

* Update docs to mention 0.5

Leak occurs when printing docs, but it would likely arise when using ASyncStaticFiles generally, just run async server with PYTHONASYNCIODEBUG=1 and warnings will start to show up.

Warning:

       /usr/local/lib/python3.6/asyncio/coroutines.py:110: ResourceWarning: unclosed file <_io.BufferedReader name='/usr/local/lib/python3.6/site-packages/apistar/static/fonts/fontawesome-webfont.woff'>
  return self.gen.send(None)

* add test for unserializable json

* raise, don't return TypeError

Fix enum validation errors.

…cuments. (#585)