v0.5.0

Added

• Google simple implementation with support for compute_instances
  (Issue #2)
• AzureRM simple implementation with support for virtual_machine(just linux) and linux_virtual_machine
  (Issue #3)

Changed

• [breaking] Remove the repeated Backend and abstracted it to it's own package
  (Pull #60)
• No cost returned when no prior exist in plan
  (Pull #61)