Terminal execution support

A user/developer should be able to call programs directly from their Grease script. This allows them to create more complex programs without needing to use or create native Grease bindings. For example, rather than creating a Grease interface for a native dependency like yt-dlp (a terminal-based youtube downloading tool, for example), we could simply call it within our Grease script with something like call_process("yt-dlp -f 140 " + my_url) (this is an example. the actual interface is still under debate).