Fix typos and style on README.

- consistently name this project as `Octokat.js` outside of code, with uppercase `O`, like the original Octokit does.
- use correct case for project names. E.g.: `Node.js` instead of `NodeJS`, `RequireJS`. Found with: https://github.com/plasticboy/vim-markdown + `set spell`.
- Where style was not consistent, i.e. two standards on same file, I followed http://www.cirosantilli.com/markdown-styleguide/ and made it consistent. In particular:
  - some headers had extra blank lines before and others not. I removed them to take less screen space.
  - break very long lines. Better for `git diff` without extra config. Some were broken and others not.