Export functionality

I'm starting to work on making exporting happen. Not at all ready to merge - I'm just curious what you think.
I want to just make the PlatformExport class have an ```export``` method and be done with it - this method seems kinda silly to me right now.
```Exporter``` can handle things common to each build, and then hands off the rest of the process to the specific platforms, rather than having them repeatedly call back and forth.
Does that make sense?