Fixed to allow Account model to be created, and updated to latest canvas
docs.

Test Plan:
  In irb, should be able to use pandarus.get_single_account(id) and get
an account object.
 Example:
  p = Pandarus::Client.new(:prefix => 'http://localhost:3000/api', :token
=> <token-for-local-canvas-here>)
  a = p.get_single_account 1
  a.name #=> should return name
  a.default_time_zone #=> should return time zone

fixes: SIS-377

Change-Id: I2321aa4edd0cfed91a63f8d85230e1e0f69f25cc