Now `camltc` uses submodules, init & update it

Looks like `opam` doesn't clone `git` repositories using `--recursive` by
default. This change makes sure the TokyoCabinet submodule is initialized
before attempting to build.
Merge pull request #6 from Incubaid/camltc-init-submodule

Now `camltc` uses submodules, init & update it