make model creation fail if head variable ill-formed
refactor boolean expression visitor to just expression
fix a string bug probably fixed elsewhere
make head expressions more expressive

specifically just allow a single binary op.
still not fully general; but this can be expanded when needed
for datalog, change project creation to apply

also make clang languages CApply compilation work properly.
Include test case for datalog parse of it
fix literal string warnings
add a clang test for binary ops in the IDB head
put project back in datalog model

for now Apply will also do column select, although
it may not have to
address comment on fluffy code
remove boolean expression visitor
tests for proper groupby creation in datalog
remove irrelecant comment
fix bug in compiler visitor
add agg+agg to syntax
make datalog.toRA work for any aggregates or expressions in head

based on discussion with dhalperi
on complex expressions in #209
Merge pull request #209 from uwescience/bmyerz-datalog-parser-fixes

Datalog: expressions in IDB head