0.4.0 WIP

Contains the changes to be included in the v0.4.0 release.

Here's an overview of the changes being included:

- [ ] Move `init` functionality into `create` and the constructor for `Internationalization`
- [ ] Message bundles are fetched by new `load[Sync]` methods which can be called numerous times to override/append to the internal message bundle and `init` process no longer involves this
- [ ] Internal configuration (based on user-specified options) are stored in a new `config` property
- [ ] Make the `Messenger` class contain only logic relating to interacting with the message bundle, merging all other logic into the `Internationalization` class
- [ ] Utilize [Underscore.js](http://underscorejs.org) (?) - Would add dependency
- [ ] Better (cleaner) way to access HTML escaping