C# support
User yowl has [an example of C# for wasm4](https://github.com/yowl/csharp-wasm4), reporting an [output wasm file size of 1283 bytes](https://twitter.com/yowl00/status/1473071184673751046), so we should add C# to wasm4.

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