Split into 3 gems

[mhaylock]

The gem has a lot of dependencies that are necessary for the whole, but I would like to be able to use certain aspects of the gem without requiring the dependencies of other parts of the gem I don't wan't to use.

I see this gem being broken down into three parts, with some proposed gem names:

• swift-playground: The CLI
• swift-playground-parser: The ability to parse existing playground files
• swift-playground-builder: The ability to create new playground files

The primary goal here is to be able to use the parser aspect independently of the dependencies of the builder or the cli.

The builder gem would be dependent on the parser gem, and the main CLI gem would be dependent on both of the other gems.