Add a *.pex parser.
It works with the files created with http://onebyonedesign.com/flash/particleeditor/
Add optional emitter param
Throw an error if the file doesn't exists.
Added different input data:
- An ID to the assets file.
- A file embedded with @:file()
- A string with the content of the file.
- A XML object.
Merge pull request #91 from mrcdk/pexparser

Add a *.pex parser.