implement liquid blocks for blockquote, pullquote, twitter, img and
youtube
test liquid block detection
document liquid plugins
Merge branch 'feature/liquid-filter', closes #115

Currently, the following tags are ported:

- blockquote -- generate beautiful, semantic block quotes
- img -- easily post images with class names and titles
- youtube_ -- easy embedding of YouTube videos
- pullquote -- generate CSS only pull quotes — no duplicate data, no javascript
- tweet -- embed tweets using Twitter's oEmbed API
warn if view name could not be located
improve reST format detection
only strip trailing newlines from post content
extend simplified BSD license to its original form