Integrate lua interpreter
These things are included in the branch:
- Support for embedding files into the resulting binary.
- Integration of lua interpreter.
- Auto-loading bunch of „modules“ from a directory.
- Convenient calling of functions inside the interpreter from C code.
- Tests for these.
There's one TODO left ‒ we may want to precompile the lua code into luac before embedding into the binary. But as there's no support for that in the OpenWRT buildroot and we check the lua syntax in tests (by auto-loading), the benefits aren't high, so I'd leave that out for some unspecified future time.