Add JSHint configuration.

- Add .jshintrc
- Add JSHint information to README

The `.jshintrc` file contains a definition for each valid JSHint option.
I've configured JSHint to be pretty lax at the moment, having it mostly
only throw errors about indentation.

Adding this file will allow anyone to manually lint their files, but it
will also greatly help developers who configure a JSHint integration
within their editors by offering immediate, contextual hints.

@photonstorm: The full definition for each of the included options can
be found on the [JSHint options
page](http://www.jshint.com/docs/options/). I wanted to leave it to you to
determine the project style.

This PR resolves #140.