Added type definitions for openstack heat templates.
Added top level function Heat for declaring a heat template
Separated type generation out into two classes - now that it sort of works, it needs to be consolidated some - too much copy-paste

TODO:
Need to make sure that the generated heat templates will validate against heat
Need to make sure that cf templates are still valid.
added device encryption options
Merge branch 'master' of github.com:howech/cfndsl into eval-context
minor tweaks to the openstack definitions
Merge pull request #58 from howech/master

Add some nominal support for Openstack Heat