Readme rewrite

I've moved out some of the contribution instructions into `CONTRIBUTING.md` and made a couple of minor changes, mainly adding links.  I'd like roughly the following sections in `README.md`:
- [ ] Summary of the project
- [ ] History of the project
- [ ] Contributing summary
- [ ] Contributors
- [ ] License and copyright

And in `CONTRIBUTING.md`:
- [ ] Summary
- [ ] Using the issue tracker
- [ ] Setting up the development environment
- [ ] Making a pull request
- [ ] Coding style
- [ ] Licensing information

I'll close #7 as it also touches the Gemfile, @Cokemonkey11 could you re-apply your Readme changes to this branch, and open a new issue for Gemfile fixes if needed?