0.3.0 WIP

Contains the changes to be included in the v0.3.0 release.

Here's an overview of the changes being included:

- [x] Generic attributes (replacing `[data-]int17-*` attributes with `[data-]i18n-*`
- [x] Remove message validation
- [x] Replace `optimize` option with `ignoreCase` (defaulting to `true`) to improve performance of placeholder lookups
- [x] Add new `optimize` and `parse` methods to `Int17` that allow messages to be optimized (unnecessary `description` and `example` properties removed) and parsed (bundles built from strings) respectively
- [x] jQuery plugin
- [x] Remove/simplify validation and/or configuration of options
- [x] Move private/utility functions into embedded class
- [x] Make code even more modular/extendible
- [x] Export core classes (i.e. make `Internationalization` and `Messenger` accessible via `Int17`)
- [x] Allow messages to be specified in options
- [x] Improve escaping to ensure extensions don't have to rewrite logic when overriding `get` etc.
- [x] Code tidy and optimizations