json-schema for .jshintrc files

Any editor/IDE supporting json-schema will be able to provide rich auto-completion for `.jshintrc` files.

![jshintrc](https://cloud.githubusercontent.com/assets/1258877/2676178/c7d96bc6-c130-11e3-968f-2e2b4ac82a25.png)

This makes it much easier to work with `.jshintrc` files as well as helping to avoid typos. A json-schema file can also be used as documentation for the `.jshintrc` file.