Fixes issues with charset moving

 - Charset would not be moved correctly with keepBreaks
 - Performance improvement due to previous method accumulating
 a large buffer in a RegExpi, which is really slow, especially
 when it would not actually find a charset declaration.
Merge pull request #55 from rrjamie/fix-charset-issues

Fixes issues with charset moving
Mentioned @rrjaime fix to @charset.
lib/clean.js: remove trailing spaces
History.md: break line