Initial implementation of Sass compiler; fixes #642

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
Add a way to prevent Sass output filename conflicts

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

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
Merge branch 'master' of github.com:getnikola/nikola into sass

Conflicts:
	CHANGES.txt
Merge branch 'master' of github.com:getnikola/nikola