Make post(path, body) work in tests

Not entirely happy with the solution as it could be tricky to notice the
args have changed order in the future but the is_binary test helps with
that
Merge branch 'master' of github.com:dynamo/dynamo into fix_post_with_body_in_tests
Added improvements to post accept hash dict
Merge pull request #174 from thiagofm/fix_post_with_body_in_tests

Fix post with body in tests + improvements
Update .travis.yml
Update .travis.yml
Test all Erlang R16B versions