[WIP] Release object for Wordpress deployments

Wordpress Release helps the deploy:wordpress task.

Release will grab Wordpress releases from wordpress.org, defaulting to the latest version if one is not specified. Release will also allow for a user specified install location via the `wordpress["install_dir"]` environment option.

Another small enhancement in this release, is that when the Wordpress plugin is first loaded, it will set up a default array for db_prefix, base_uri, etc.

__What it fixes:__

#16, #15, #11

__What's left:__

* [x] - Fix compatibility mode to work with the custom install_dir
* [x] - Provide a custom install_dir for plugins __??__
* [x] - Provide a custom install_dir for wp-content __??__