Auth and Rate Limiting infrastructure #31

[thinkjrs]

When merged, this should add a new Auth and other classes to handle the following:

• Initial lazy-loading of the token from a refresh_token parameter or environment variable.
• Proper authentication token added to each request, using the requests auth built-in.
• Decorator for base api call such that each request also monitors so that it
  1. Self-updates the token when expired
  2. Self-halts the client request if the limit has been reached

  I'd really like to get a queue going for requests on halting due to insufficient remaining api calls that continues after refresh!