feat(compiler): Ignore compiler warnings

[alex-snezhko]

match (true) {
  true => void
}
let a = [> 1, 2]
a[1.5]

# will warn
grain compile main.gr
# will not warn
grain compile main.gr --ignore-warnings=all
grain compile main.gr --ignore-warnings=partialMatch,arrayIndexNonInteger

Closes #163

[ospencer]

We discussed this on Discord and decided that for now, we don't want the command line flag. For what's needed for Silo, it just needs to be programmatically configurable, but ideally we'd allow disabling a warning using a comment.

[alex-snezhko]

@ospencer do we want comments or attributes for this?

[ospencer]

Attributes would be a little nicer, but we don't currently support attributes on arbitrary nodes, and that's actually kind of a hard problem. If you want to pair on trying to make that happen we can do that in another PR.