Support for an API

I think it's very useful to have a simple REST based API for JSBin that can be used for retrieving bins, creating bins, and creating revisions for specific users or anonymous users.

I have included options to turn off anonymous API usage in the config.default.json file meaning only users explicitly assigned API keys will be able to use the API.  I have also added the option to enforce TLS connections for all API requests to protect a sensitive API key.