Fix blank options

Compass may fail at compiling if the spawn command is passed a blank string which will happen for non-default values for the `opts.comments` and `opts.relative` options. 

The solution is to move option collating outside of the spawn command so if the option isn't setting a switch, it will not do anything.

I've also added logging to provide the user with feedback as to what is going on when the middleware is trying to compile their stylesheets.