Add support for ebs volumes
Add tag support for resources where this information is not available
with the Enum method (ELB for instance)

To achieve this:
*addition of a tags_spec Meta property with the method to
retrieve tags and the jmespath
*Modification of the tags methods in the AWSResource class
Add parent property to volumes (id of instance it is attached to
    or None if not attached)
Add simple tests for volume resource
Add unit testing for loadbalancers including the retrieval of tags
through the tags_specs property
Merge pull request #29 from lbernail/develop

Support for EBS volumes and tags for resources where describe methods is not sufficient