Support for absolute URLs in HTTP requests

The requests with absolute URLs were not supported.
A request such as

GET http://localhost:5100/healthcheck HTTP/1.1

makes PATH_INFO receive http://localhost:5100/healthcheck instead of just /healthcheck.
I believe this can be fixed in serving.py by testing if path starts with http:// and discarding the domain part before setting PATH_INFO.

Please take in consideration just the file serving.py, the other files are related to shanewholloways version that I forked previously (and shamefully I did not know how to remove from this pull request).