Ref #933 - dev and build tasks for Grunt

Dev: don't minify
Build: minify, lean Modernizr build

Dev assets will load if you have defined your WP_ENV as development
If you don't use Bedrock, you'll need to add this to your wp-config.php:

define('WP_ENV', 'development');

TODO: lib/scripts.php shouldn't need to be committed for changes after
running the version task

.gitignore

@@ -2,6 +2,7 @@
 # Read about how to use .gitignore: https://help.github.com/articles/ignoring-files
 node_modules
 assets/vendor/*
-assets/css/main.min.css.map
-assets/css/*main.*.min.css
-assets/js/*scripts.*.min.js
+assets/css/main.css.map
+assets/css/*main*.css
+assets/js/*scripts*.js
+assets/js/vendor/modernizr.min.js