WASM build target support

[imthatgin]

This request is related to the following issue with bevy_mod_scripting: makspll/bevy_mod_scripting#166

It would be great to be able to run lua scripts in web apps that integrate bevy_mod_scripting, and it seems to depend on this crate supporting it.

[alerque]

I don't know how far or close this crate may be from supporting it, but this would be a very welcome feature for several of my projects as well. I know there are other Lua VM's that can be compiled into WASM, so at some level this should be feasible, but it also probably isn't trivial.