Remove dependency on the `marisa-build` executable.

[cessen]

Right now we have to call the marisa-build executable as part of the dictionary build process, which is annoying because it requires the user to install a completely separate tool. It would be great to get rid of that dependency.

At the moment, I don't think there are any existing crates for handling the marisa format, so this would be a somewhat major undertaking--we'd need to either write bindings for the marisa library or write our own marisa file builder.