Add support for alternate compilers (e.g., guida)

[dbj]

Add support for alternate compilers (e.g., guida).

Please add ability to switch out the standard elm compiler for guida, for example, through the elm-watch.json config file.

[anka-213]

Does it work if you add an alias mapping "elm" to "guida" where you run elm-watch? Or are there backwards-incompatible changes in guida that would confuse elm-watch if you do that?

Example:

PATH=/path/to/fake-elm:$PATH elm-watch hot

where /path/to/fake-elm is a directory that contains e.g. a symlink to guida or a shell script running guida with the name elm.

[lydell]

I would be surprised if any alternative compiler works.

I think it’s better if guida adopted my patched core packages that support hot reloading instead. The branches are listed here: lamdera/compiler#65. (I want to make PR:s for that later. Edit: elm/core#1155)

On top of that Guida would need to also build a watcher, but that feels easier.