Adding podspec.

A few issues worth noting:
* This project doesn't use semantic versioning, which cocoapods prefers
* The License isn't clear. Some files have MIT boilerplate, others do not, and
  the README lists a license as a "todo"
* The code has a few errors picked up that whilst aren't failures (mostly int
  precision related) still should be addressed
* The overall structure of this code could be cleaned up to be more compliant to
  what cocoapods is expecting, even if its users aren't using it.
Adding MIT License

Like my last commit, this is my assumption given the previous boilerplate found
in some of the source code.