Upgrade downsize to 0.0.4

refs #1095
- added new unicode test to excerpt helper

This addresses issues (e.g. #1095) with unicode languages and the excerpt/content helper failing to limit the content by words. Downsize 0.0.4 now uses XRegExp (https://github.com/cgiffard/Downsize/pull/3) in order to support matching unicode strings. This allows downsize to work on languages like greek or russian properly.

Some more thought will have to be put into supporting CJK since the notion of a "word" is different there.