literals don't crash in the new vc generator
changed the names of the proof rules to be consistent
fixes a crash with empty locations
true goals don't show up in the web interface
Merge pull request #132 from yushan87/vcgen-fixes

Vcgen fixes
now it should stop generating vcs for requires true
Merge pull request #133 from yushan87/minor-fix

now it should stop generating vcs for requires true