ported backward compatibility classes and properties from php-mf2

Filled in the backward_compat module with class mappings adappted
from php-mf2. BeautifulSoup tags are augmented with mf2-style
classes before the usual parsing takes place.
fix encoding issue: utf-8 characters in backcompat comment
Merge pull request #37 from kylewm/backcompat

 ported backward compatibility classes and properties from php-mf2