Generalize String criteria matching

[earboxer]

Closes #306

Most string fields have been changed to support

• Regex matching [app-name~=D..o]
• Not equal to [summary!=""]
• Bare specification [summary] (equivalent to [summary!=""])
• Bare negation [!summary] (equivalent to [summary=""])

[earboxer]

I included the operator OP_NONE, but it's not being used.

Originally I was thinking this could replace the 'spec' definitions, but didn't dig deep enough to see if this is the case or not...