Add mean FFI call latency by arity by interpretation microbenchmark
bench_micro: more descriptive graph legends
bench_micro: test up to 15-ary, move chart key to top left
Merge pull request #222 from dsheets/bench_micro

Add mean FFI call latency by arity by interpretation microbenchmark
Add bool type corresponding to the llvm i1/ C99 bool

The idea is to find a way to represet the llvm i1 type, since llvm
ExecutionEngine also uses libffi now. It's a single bit of information,
but we're using ctypes_copy_uint8, one quantum of memory addressing is 8
bits; 7 bits are wasted. This patch is mostly a nice-to-have, since we
can always represent the data as a char and coerce it into a bool
using (bool_of_int (Char.code (getf value lang_bool))).

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>