Initial work on porting to DigitalOcean's APIv2.

Droplet creation and other actions are fully functional. Other
objects are not yet ported.

* digitalocean/Droplet.py:
 - Fully ported.
* digitalocean/Event.py:
 - Replaced by digitalocean/Action.py
* digitalocean/Manager.py:
 - __call_api() and get_all_droplets() are ported. Other
   funtions have not been touched.
Port Region object and get_all_regions().
Port Size object and get_all_sizes().
Port digitalocean/Image.py, get_all_images(), get_my_images(), and get_global_images().

Also introduces handling of pagination.

Note that while this has ported existing image related functions, it
hasn't yet exposed `/v2/images/$IMAGE_ID/actions/$IMAGE_ACTION_ID`
or renaming images which is now possible.
Support renaming Images.
We're POSTing not PUTing, so call it that.
Initial work on Domains.
Fix hair pulling stupidity. :boom:
Complete porting of Domain.
Port SSHKeys.
Port the examples in README.md
Merge pull request #35 from andrewsomething/apiv2

Port to APIv2