Add support for Procs
Revert "Add support for Procs"

This reverts commit f87e98810ce06624dc0e5dca3d567478b0e1a495.
Evaluate in varia model, not attributes
Only evaluate Procs in VariaModel
Add additional proc test for runtime evaluation
Merge pull request #2 from sethvargo/support_procs

Add support for Procs