chore(cmath): use cmake instead of make
fix(cmath/sin.c): suppress warnings
feat(cmath): add simplified.c
feat(src/cmath/cil2smt): basic implementation

1. The Simplify extension is not strong enough.
feat(src/cmath/cil2smt): add ssa transformation.
chore(cmath/cil2smt2): update Makefile; rm _tags; build native obj
chore(cmath/cil2smt2): update .gitignore
chore(cil2smt2): move src/cmath/cil2smt2 => src/cil2smt2
chore(cil2smt2): move testfile sin.c to test/
chore(cil2smt2): update Makefile
feat(cil2smt2): use cmd-line option/parsing
chore: move .merlin
tests(cil2smt2): add more tests
fix(cil2smt2): disable dumpfile
fix(cil2smt2): make unique "not now" message
fix(cil2smt2): fix a bug in handling "if-then-else"
feat(cil2smt2): add smt2.ml
feat(cil2smt2): print out smt2 header and footer
feat(cil2smt2): add var_decls in output
feat(cil2smt): support cast expression