Release script with automatic version numbering

Use one of the following commands to create a release build and bump the version no:

```
gulp release --ver 'major'
gulp release --ver 'minor'
gulp release --ver 'patch'
```

The release will be committed and tagged with the version number automatically.

Please merge #59 before merging this pull request.
Since this depends on `version-file` and `version-file` depends on `version` it bumps the minor version everytime `npm install` is issued. I don't think `version-file` should depend on version. It should simply take the current version (from `package.json`) and create the VERSION file.