Refactored editor.js

I just felt like refactoring your `editor.js` ;)

- Refactored editor.js
- Tweaked button layout
- Updated selection handling (freaking browser events…)
- Merged basic [Grunt.js fork](https://github.com/tholman/zenpen/pull/39) and removed unused cases
- Merged embedded edtior fork and removed it again
- Added .jshintrc and .jshintignore files for clean code
- Included [underline feature from other pull request](https://github.com/tholman/zenpen/pull/57)
- Included [ret variable scope to local pull request](https://github.com/tholman/zenpen/pull/55)
- Added option for disabling unwanted style features `new ZenPen('editor', ['link', 'bold', 'italic', 'quote' /*, 'underline' */]);`
- Added Markdown export to index site using [to-markdown](https://github.com/domchristie/to-markdown)