feature request: Add `ignore dir` command line arg

[Eoksni]

Use-case:
I have a project structured like so:

myproject
  \_ app
    \_ Main.hs
  \_ src
    \_ Lib.hs
  \_ test
    \_ test.hs

So if I do halive app/Main.hs, it gets reloaded on any change in the test dir, which should not happen - tests have no influence over the main app.

And if I do halive Main.hs from app dir, it doesn't get reloaded on changes in the src.

So having an ignore feature would allow me to exclude test files from restarting my app.

Btw, this project is super cool! Works really nice and extra fast reload.