added support to configure sass compiler, sassc is way fast
added myself to AUTHORS.txt and updated CHANGES.txt
Merge pull request #940 from ermeaney/sassc_support

added support to configure sass compiler, sassc is way fast
fix small bugs

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
proper shell= support for less/sass, fix #939

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
implement #940 (alternate *ss compilers) for less

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>