Remove bundle task.

gulp-bundle is deprecated. gulp-useref now has the ability to concatenate assets inside build blocks and pass them to the stream. Minification of assets is now handled in the gulpfile instead of gulp-bundle. gulp-filter is required to handle filtering the stream for asset minification.
Merge pull request #37 from jonkemp/gulp-bundle-deprecate

Remove bundle task.
Update USAGE

fixes #39
[gulpfile.js] fix small formatting issues.