FIX Mustache AMD and global identifier definition

This pull request tries to solve compatibility errors that occur when RequireJS (or CommonJS) is loaded on the page and mustache.js is also loaded but as an external module (used by a third party plugin for example).

The fix is based on how jQuery implements AMD and defines the jQuery and $ global identifiers:

```javascript
// Define a local copy of jQuery
var jQuery = function( selector, context ) {
	...
};

...

if ( typeof module === "object" && module && typeof module.exports === "object" ) {
	// Expose jQuery as module.exports in loaders that implement the Node
	// module pattern (including browserify). Do not create the global, since
	// the user will be storing it themselves locally, and globals are frowned
	// upon in the Node module world.
	module.exports = jQuery;
} else {
	// Register as a named AMD module, since jQuery can be concatenated with other
	// files that may use define, but not via a proper concatenation script that
	// understands anonymous AMD modules. A named AMD is safest and most robust
	// way to register. Lowercase jquery is used because AMD module names are
	// derived from file names, and jQuery is normally delivered in a lowercase
	// file name. Do this after creating the global so that if an AMD module wants
	// to call noConflict to hide this version of jQuery, it will work.
	if ( typeof define === "function" && define.amd ) {
		define( "jquery", [], function () { return jQuery; } );
	}
}

// If there is a window object, that at least has a document property,
// define jQuery and $ identifiers
if ( typeof window === "object" && typeof window.document === "object" ) {
	window.jQuery = window.$ = jQuery;
}
```