Improve usage and support

- [x] Closes #15. Support loading .jsbeautifyrc from Project directory.
- [x] Handlebars support, https://github.com/donaldpipowitch/atom-beautify/issues/13
- [x] Fix bug: Custom configuration is ignored and overridden, https://github.com/donaldpipowitch/atom-beautify/issues/16
- ~~Specs and Travis CI config, https://github.com/donaldpipowitch/atom-beautify/issues/18~~
- [x] Can now beautify new files that have not been created/saved., https://github.com/donaldpipowitch/atom-beautify/issues/19
- [x] Sass and LESS support, see #20