fixed ParseTextField postprocessing, added genre field to MultiNLI

[putama]

• Fix ParsedTextField postprocessing that still accepts three args instead of two
• Added an option for ParsedTextField to whether to reverse the sentence as postprocessing
• Include parse trees for testing and reverse postprocessing test

[mttk]

@putama could you please fix the flake errors reported w.r.t. some line lengths and (just for my sake) elaborate on what was the error with the postprocessing fix?

[putama]

Hi. I found that on field.py line 290, they changed the call to postprocessing function into only 2 arguments. This was the quickest fix I could think of.

[mttk]

Ok, cool. Could you just fix the last flake complaint (IMO, just if/else the function call and leave the lambdas as arguments)

[putama]

Done, thanks. Could you tell what the latest unsuccessful check was about?

[mttk]

Functions are preferred to lambdas in PEP8 due to easier stack tracing (https://stackoverflow.com/questions/25010167/e731-do-not-assign-a-lambda-expression-use-a-def).
They seem reasonable here as it's unlikely to use them again so the hack around that check is to put them as default args in function calls, where they're allowed.

Thanks a lot for the fix!