Firecracker-v0.2.0

• Users can now enforce that an emulated block device is read-only via the API.
  To specify whether a block device is read-only or read-write, an extra
  "permissions" field was added to the Drive definition in the API.
  The root filesystem is automatically mounted in the guest OS as ro/rw
  according to the specified "permissions". It's the responsibility of the user
  to mount any other read-only block device as such within the guest OS.
• Users can now stop the guest VM using the API.
  Actions of type 'InstanceHalt' are now supported via the API.
• Added support for getDeviceID() in virtIO-block.
  Without this, the guest Linux kernel would complain at boot time that
  the operation was unsupported.
• STDIN control is returned to the Firecracker process when guest VM is inactive.
  Raw mode STDIN is forwarded to the guest OS when guest VM is running.
  'blockdev --report' and when checking /sys/block//ro).
• Users can now interrogate Instance Information (currently just instance state)
  through the API.