Nelua support
[Nelua](https://nelua.io/) can compile to WebAssembly using [Emscripten](https://emscripten.org/). An example can be found here: https://github.com/edubart/nelua-game2048

- [x] `w4 new`: Add new project template
- [x] `w4 watch`: Add new filename suffix + build/run support
- [x] `w4 png2src`: Add new language parameter
- [x] Website: Setup documentation
- [x] Website: Translated code snippets for all guide pages
- [x] Website: Add code to Snake tutorial