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
Improved value-class-pattern parsing for datetimes, based on php-mf2
Merge