allow custom engine factory construction in .less preprocessor (fix #242)
allow custom engine factory construction in .less preprocessor (fix #242)

0liver/SquishIt,jetheredge/SquishIt,AlexCuse/SquishIt,0liver/SquishIt,AlexCuse/SquishIt,Worthaboutapig/AC-SquishIt,jetheredge/SquishIt,jetheredge/SquishIt,jetheredge/SquishIt,AlexCuse/SquishIt,AlexCuse/SquishIt,Worthaboutapig/AC-SquishIt,0liver/SquishIt,Worthaboutapig/SquishIt,jetheredge/SquishIt,wolfgang42/SquishIt,Worthaboutapig/SquishIt,wolfgang42/SquishIt,jetheredge/SquishIt,0liver/SquishIt,farans/SquishIt,0liver/SquishIt,AlexCuse/SquishIt,Worthaboutapig/AC-SquishIt,farans/SquishIt,AlexCuse/SquishIt,farans/SquishIt,Worthaboutapig/SquishIt,Worthaboutapig/SquishIt,Worthaboutapig/AC-SquishIt,wolfgang42/SquishIt,wolfgang42/SquishIt,farans/SquishIt,Worthaboutapig/SquishIt,wolfgang42/SquishIt,Worthaboutapig/AC-SquishIt,farans/SquishIt