In LessphpFilter, allow formatter to be changed.
In LessphpFilter, allow comments to be preserved in the output.
Add tests for LessphpFilter's 'formatter'.

https://github.com/amyboyd/assetic/commit/180c7dbe3b1a1a78348188682b76cf3d479f5320
Add tests for LessphpFilter's 'preserve comments'.

https://github.com/amyboyd/assetic/commit/3351d6386be3452e7529a3dc477784da8688a3d6
Merge remote-tracking branch 'amyboyd/master'
cleaned up lessphp