Allow passing arbitrary command line flags to klee and kleaver
when running llvm-lit. This is done by doing something like

$ cd test/
$ llvm-lit --param klee_opts=--xxx --param kleaver_opts=--yyy .

This would pass "--xxx" as an extra option to KLEE when running
tests and would pass "--yyy" as an extra option to kleaver when
running tests.

This feature has been added to make it easy to pass different flags to
KLEE or Kleaver without needing to modify tests or recompile KLEE with
different defaults (yuck!).
Merge pull request #100 from delcypher/pass-param-llvm-lit

Allow passing arbitrary command line flags to klee and kleaver when running llvm-lit