Add RingBuffer.swift.

Basic RingBuffer class.
Add basic RingBuffer tests.

They really need better tests, but I'm still getting used to this.
Un-ignore default workspace.

Add .DS_Store, trashes, etc. because they're in my personal ignore file
but not in the repo's.
Update project file.

- Adds the license text.
- Adds the RingBuffer and test.
- Reorders files.