Option to select input files

[Deraen]

Related #17

Currently sass4clj compiles any non-partial files (i.e. not starting with _) in source-paths. It could be useful to select input files using option in some cases, like if the source-path contains some Sass libraries which include non-partial files.

Things to consider:

• API & CLI option:
  • (build {:inputs ["foo.scss" "bar.scss"]})
  • clj -Asass -i foo.scss -i bar.scss
  • List of paths relative to source-paths? or relative to current directory?
• Boot option
  • No source-paths, source-paths is the fileset.
  • Input paths has to be relative to fileset.
• Lein option
• Implement the same option for https://github.com/Deraen/less4clj/