Windows builds fail due to Shelly being broken on Windows

[phlummox]

Versions of Shelly from 1.8.0 onwards are broken on Windows (and thus builds for Hup are broken, too): see this bug. This was only recently fixed in the Shelly github repo, and a fixed version hasn't made it onto Hackage, yet.

A workaround for this would be to use the Shelly Github repo itself as a dependency (possible for Stack, I don't know whether cabal permits this yet), but for CI purposes, I'm just going to refrain from using recent versions of Shelly til the fix makes it onto Hackage.

So this means Shelly 1.7.2 is the most recent, non-broken version on Hackage; but that version's dependencies (in particular, from what I can tell, time (>=1.3 && <1.9)) apparently stop it being built with versions of GHC more recent than 8.6.5. Again, there are probably fixes for people who really want to get it built (e.g. loosening the bounds), but for CI purposes, I'm just not going to build on versions of GHC more recent than 8.6.5, until Hackage has a working version of Shelly again.

So my current task for Hup is to get CI builds working on Linux, Mac and Windows using GitHub Actions. Some non-x86 architectures and static binaries would be nice, too. We'll see.