Merge pull request #23 from kylewm/master

Basic Value-Class-Pattern support & a Travis-CI configuration.
fixes #22
uses find_all not recursively. removed is_tag() from dom_helpers
include filtering in to_dict and to_json. resolves #18
always return proprty names. resolves #15
added parsing of input and data in url property
Improved value-class-pattern parsing for datetimes, based on php-mf2.
Added test cases for parsing dates with value-class-pattern
Merge in changes from master
Fix python2 compatibility by using element.decode_contents() to render the contents inside a BeautifulSoup4 tag