I use this in case I just want a quick UI for a project of mine, and don't want
to create the entire Obelisk structure, not having the need for js or android
code generation. Having this in my ~/.config/nixpkgs/overlays, I can just add
reflex and reflex-dom to my .cabal file, and cabal new-build it.
Currently, reflex and reflex-dom use the latest hackage release, while I
have slightly patched reflex-dom-core to make it compatible with ghc 8.6.4.