Prefer to pull title from document body if specific classes are present

https://www.readability.com/developers/guidelines#publisher references specific standard class names that can be used by publishers to denote the proper article title without any additional cruft that may be present int he title tag. The class instapaper_title also seems to be common (articles on theverge.com) for similar reasons.

I've updated title extraction to prefer these classes if present in the dom over the \<title\> tag. 

Also included is the inclusion of  a readability specific convention (same link as above) for ignoring sections of the dom similar to instapaper_ignore.