Fix #14: Parse incomplete HTTP status codes

The fix works but the changes needed for testing it
are probably not what you want. I suppose in order to
prevent any changes in hackney_http, I'd need to do the
tests inline but as I didn't see this I decided
to make an outside test working.

However I think you might not like these changes, therefore
please guide me what would be the best option.
Merge pull request #15 from mweibel/issue-14-fix-http-status-code-parsing

Fix #14: Parse incomplete HTTP status codes