Fixed #202 -- adding content-type header broke registration.
added knife-digital_ocean to Gemfile
added digital ocean to provider choices
added a standardized way of adding new providers

this way, developers just need to provide a new
dict to the function, containing al of the
provider discovery code
added dop to the requirements list

this is a python package for communicating with
the Digital Ocean API
added snapshot/controller provisioning scripts
added digitalocean provider code
Merge branch '73-digitalocean-provider' of github.com:bacongobbler/deis into 73-digitalocean-provider