Added some extra tests and tweaked `IntrospectorHelper.import_from_string`
Added rstLikeDocumentationParser tests
Introduced documentation formatters and some other minor changes.
Also:
 - [Global] Replaced `rest_framework_swagger` from imports and replaced it with `.`
 - [Settings] Added `DOCUMENTATION_FORMATTER`
 - [Settings] Renamed `DEFAULT_DOCUMENTATION_PARSER_CLASSES` to `DOCUMENTATION_PARSER`
 - [Settings] Renamed `DEFAULT_URL_PARSER_CLASSES` to `URL_PARSER`
Updated README