Issue LIBCLOUD-494: Add extension methods to support additional EC2 image
calls. The first is ex_copy_image which is used to copy Amazon Machine
Images between regions and the second is ex_create_image which can be
used to create an AMI from an EBS backed instance.

Closes #222.

Signed-off-by: Tomaz Muraus <tomaz@apache.org>
Fix docstring issue which caused failed documentation build.
Update CHANGES.