Code clean up, added positional arguments support.
Rate limit support. Custom headers support.
Added thread safety + minor fixes.
Exceptions raise on error response from aftership API
Included API v3 specifics. Custom error handle type, and API class — APIv3.

APIv3 main features:
— Returns 'data' dictionary on success (strips 'meta dictionary').
— Accepts lists and datetime objects as input parameters (converts them to comma-separated strings and ISO 8601 strings).
— On return, converts ISO 8601 strings to datetime.
Packaging info and pypi/github/package documentation (in progress).
Merge pull request #2 from korshunov/master

Updates