Add CommonJS and AMD Compatibility + addChar()

In the presence of CommonJS / AMD, kineticjs-editable-text will return an object containing an ```init()``` method. KineticJS gets passed as an argument to ```init``` and will be extended with ```Kinetic.EditableText```. An example can be seen [here](https://github.com/mjhasbach/ceros-snake/blob/96f1b3abc631d83b5447cbfb36f03d9a77f49cfd/js/libs/highScores.js#L215).

I also added an ```addChar()``` method, which allows characters to be added to the kineticjs-editable-text field programmatically. ```addChar()``` is [used internally in kineticjs-editable-text](https://github.com/mjhasbach/kineticjs-editable-text/blob/2e098be41a0c18e86ba1afc54c21c1d6034eeade/js/kinetic.editable.js#L640) and an external example can be seen [here](https://github.com/mjhasbach/ceros-snake/blob/2ebae4156f1cd72afc90fdf4e0667de8264888b2/js/libs/events.js#L192).