* mostly restored the tiled importer unit tests
* code cleanup
* code cleanup
* almost got tiled maps serialization independent of the content pipeline
* refactored the tiled map content importer so that tiled maps can be loaded at runtime
* code cleanup
* removed nuspec files
* experimenting with an XML based GUI markup parser
* a few more markup parser features
* finally got a working open file dialog
* experimenting with markup bindings
* attached properties
* working on the gui stuff again
* working on a better textbox
* multiline textboxing
* new text box is really coming along
* removed the content explorer experiment
* restored the old gui demo back to the way it was before (for now)
