TODOs and Remarks

handling of SIGTERM and SIGUSR
add support for RC/alpha/HEAD versions
redo/rethink how tool tags works
mirror support
checksums
check for new version on start
tarball tags as well as version tags?
--copy-compiler-tools
installing multiple versions in parallel?
exception handling (checked exception library? Maybe effects system all the way?)
how to version and extend the format of the downloads file? Compatibility?
how to propagate updates? Automatically? Might solve the versioning problem
installing musl on demand?
interactive handling when distro doesn't exist and we know the tarball is incompatible?
ghcup-with wrapper to execute a command with a given ghc in PATH?
maybe add deprecation notice into JSON