Feature Parity with HTTPolice

[pevalme]

Most of the errors detected by HTTPolice can be detected by this tool by adding the proper regular expression into one of the flex sub-parsers.

[pevalme]

Commit 6f4a864 implements the needed regexp and grammars to detect almost every single error detected by HTTPolice.
However, there is still some work to do here.
The README includes a classification of the errors to make easier to see if an error is already implemented.