CommonJS support

CommonJS support for npm & browserify.

Example Usage (browserify & superagent):

```javascript
var Raphael = require('raphael');
require('raphael-svg-import-classic');
var ajax = require('superagent');

ajax.get('assets/levels/level1.svg').end(function(err,res){
	var paper = Raphael(10, 10, 800, 600);
	var newSet = paper.importSVG(res.xhr.responseXML);
});
```