Code cleanup, comments, analyzer warnings.

@Raizlabs/maintainers-ios This is just some cleanup of this repo.
- Adds light commenting to all non-demo headers.
- Fixes some analyzer warnings.
- Removes Dependency on PCH file.
- some code style updates.

Any input around the content in comments/code style can just be made on this branch, unless a discussion is desired.
`Subclasses must override this`