Support GET requests for submitting code

[NattyNarwhal]

I'm running a community with Zulip, and one useful feature is the code playgrounds. That works by constructing a URL with the code in a query parameter (i.e. /run_php?code=(urlencoded php)), so a user can just click run on a code block to be taken to the playground. However, this needs it to be accessible via a GET method; currently 3v4l only supports a POST submission.

[SjonHortensius]

I'm not very enthusiastic about this - I'll think about pre-filling the editor with the given code but there definitely won't be an auto-submit as the abuse that brings will be endless

[NattyNarwhal]

Pre-filling without running sounds good. It also doesn't necessarily have to be a query parameter, it just needs to be part of the URL.