Merge branch 'master' of github.com:JanDC/critical-css

Updated twigwrapper dependency to 0.4

Reverted purging html store, since it would mess with subrequests

Purge the html store after critical css is build

Lowered the minimum requirement of 'doctrine/cache' to 1.6, while all…

…owing for more recent versions to be used

Lowered the minimum requirement of 'masterminds/html5' to 2.2, while …

…allowing for more recent versions to be used

Implemented doctrine cache interface to speed up asset retrieval

Moved to an html5 document abstraction to resolve encoding issues

Experimental: force the processed document to be unicode

cleanup