Configurable severity level mapping

[KillyMXI]

This is similar to carymrobbins/intellij-haskforce#194
I don't want HLint messages to be shouted (underscored in red) as if they're actual parsing errors.

It will be nice to have a setting for mapping between HLint and VSCode severity levels.
For example:

// Mapping between HLint and VSCode severity levels (possible values: "error", "warn", "info").
"haskell.hlint.errorLevel": "error",
"haskell.hlint.warningLevel": "warn",
"haskell.hlint.suggestionLevel": "info"

So it will let me change them to "warn", "info", "info".

[AlexeyRaga]

I second that, is it possible to underscore in green?
I see that screenshots show green, but my VSCode always has it red.