Update gulp-ruby-sass to 0.7.1

Necessary for updated styles task.
Reduce to a single S/CSS task and watcher

- Outputs all Sass / CSS to .tmp
- Only compiles Sass files in the folder root Sass directory and those named
  specifically. In order for `changed` to work, users should only add files that
  have output files to their styles task, and let gulp-ruby-sass figure out the
  dependencies.w
Merge pull request #314 from robwierzbowski/rw/single-sass-task

Bump gulp-ruby-sass to 0.7.1, reduce to single Sass task