begin Z3 integration

- Slow as hell: needs a translation hashmap between corestar expressions
  and Z3's
- Z3 bindings and libs not included. Here are steps to get them. You'll
  need to edit CoreStar's Makefile to reflect the new location :/

1. Download the ml-ng branch from codeplex (can't find how to link to
   specific branches, so link not included...)

2. mkdir z3 && cd z3 && unzip ../z3-[latest commit].zip

3. Then unless you're on windows you need to run dos2unix configure

4. ./configure && cd build && make

5. ./configure --ml && cd build && make ml

'make install' would also install the new version of Z3 (but,
unfortunately, not the ocaml bindings...).
memoize the translation of coreStar expressions into Z3 expressions

and with that we are faster than the pipe implementation \o/
import Z3 libraries and OCaml bindings

hopefully it's enough to have a LICENSE.txt in the directory, though we
should probably say which files it covers.

this was horrible to set up properly and I hope I never have to do it
ever again.
export OCAMLPATH in the Makefile

typing "make" should work and find Z3 automatically now...