doc: add travis build status link
Update AUTHORS and .mailmap
Bump to version 2.1
build: set SONAME in shared object file

Fixes #151.
Add function http_parser_version().

Fixes #115.
Do not accept PUN/GEM methods as PUT/GET.

* Encountering them returns an error, `HPE_INVALID_METHOD`
* Tests have been added.
Further request method check strengthening.