WP CLI integration

I would like to ship some WP CLI commands with this library. I would like to provide the following:

- [ ] Easy installation (requires closing #26)

 ```bash
wp plugin install whatever-i-title-this-thing
wp memcached install
 ```
 
 This would handle moving/symlinking the file into place and adding the basic config to wp-config.php.
- [ ] Test configuration

 Add a command to test if certain parts of the configuration are set correctly. It could check for:
 - [ ] PECL memcached availability
 - [ ] Memcached daemon availability
 - [ ] Memcached is available from PHP
 - [ ] WP object cache is storing content

- [ ] Stats - dump basic Memcached stats via the nicely formatting WP CLI tables

- [ ] Check for the [go-derper](http://www.sensepost.com/blog/4873.html) vulnerability (i.e., make sure 11211 or whatever port is being used is closed)