Add caching for previously linted files

Incorporated cache-swap as a file based persistent swap for previously
successfully linted less files.

- turned off by default
- adds a cache option with some opportunities to tweak where the files
are cached
Merge pull request #13 from jgable/cacheSuccess

Add caching for previously linted files
Prepare 0.16.0 release
Update package.json.

* sort deps by name for easier maintenance
* update link to LICENSE.md
Update all dependencies to their latest versions.