Integrate crab into Sally

[dddejan]

I've added some boilerplate to the "ai" branch.

Notes:

• The code for crab integration should be added to src/ai/crab/crab.{h.cpp}.
• Any options for the module should be added to src/ai/crab/crab_info.h and they will automatically be available from command line.
• We try to use regular c++ features, if crab is using new c++ features they should only be used within crab.cpp so that they don't leak out to the rest of the project.

[dddejan]

Here is an example how to run the code

dejan@hilbert:~/workspace/sally/build$ ./src/sally -v 1 --debug crab --no-lets  --ai crab ../test/regress/ic3/example0.mcmt
[2017-03-06.11:45:03] Processing ../test/regress/ic3/example0.mcmt
[2017-03-06.11:45:03] Crab: starting
crab: I = (= |state_type::state.x| 0)
crab: T = (= |state_type::next.x| (+ |state_type::state.x| 1))
[2017-03-06.11:45:03] Crab: done
Engine needed to do a query.

• -v 1 is the general message verbosity (to be used with MSG() macro)
• --debug crab is the trace option (to be used with the TRACE() macro)
• --no-lets is for printout without the let construct
• --ai selects crab as the abstract interpretation engine