add python3 support

[AlJohri]

fixes #28 and #30, replaces #29 and #31

• adds python 3 support via future: futurize --both-stages --write --nobackups congressionalrecord
• add PyOpenSSL via requests[security] to setup.py since there's an explicit dependency on PyOpenSSL in the code
• add future as a dependency in setup.py
• add unicodecsv as a dependency in setup.py
• fixes test_content_length test case
• change requirements.txt to rely on setup.py for dependencies since they were getting out of sync
• add python 35 and 36 to travis
• rename congressionalrecord2 to congressionalrecord
• change url from https://github.com/nclarkjudd/congressionalrecord2 to https://github.com/unitedstates/congressional-record

[nclarkjudd]

Looks good on first pass. Will take a second look this evening but probably this will get merged tonight superseding #29 . Thank you for taking the time.