Add support for the current set of CFN pseudo attributes.

As listed in http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/pseudo-parameter-reference.html

Renames no_value() to aws_no_value() for consistency with the other
pseudo attributes including the existing aws_region().
Don't break backward compatibility.
Log a warning when using deprecated functions.
Version bump.
Merge pull request #21 from bazaarvoice/ssmith-pseudoattrs

Add support for the current set of CFN pseudo attributes.