In PSA output label warnings and errors as such

[fsoikin]

Description of the change

Fixes #1148

The outputs now look like:

[WARNING 1/4 ImplicitImport] src/Main.purs:3:1

[ERROR 1/2 TypesDoNotUnify] src/Foo.purs:4:5

Checklist:

• Added the change to the "Unreleased" section of the changelog
• [ ] Added some example of the new feature to the README
• Added a test for the contribution (if applicable)

[f-f]

Patch is good, but I wonder if we should expand the texts to be WARNING and ERROR? It's no strong opinion though, just reads better to me.

[fsoikin]

I have no strong opinion either. Changed to "ERROR" and "WARNING".