Add some symbols to punctuation in strip_punctuation

[remusao]

Hi,

Since " and ' are considered punctuation in English, I thought it would be a good idea to add this characters in the function strip_punctuation! in the preprocessing module. I don't know if there is a reason for not including them in the regex, but I needed them in a project of mine, so here is a patch if you think it could be useful for others too.

Bests, Remusao