API Refactor

Just some small adjustments to the API to make everything smoother.

- Eliminate callbacks because promises are better
- Expose `Ship` as a class, makes persisting state easier, less repetition
- Add a couple commands for checking and writing config files
- Adjust deployer list to more accurately reflect our priorities
- Reword some pieces of the readme to have it read smoother

Then, complete rewrites of the heroku and github pages deployers to make them work smoothly with the new API, and eliminate external command line dependencies.