Default Lvl is LvlCrit

[kevinburke1]

If I write var x log15.Lvl there's not a good way to distinguish between unset and Crit, since Crit is 0.

The usual way to handle this with protobufs is to set e.g. LvlUnknown as the first iota value. Unfortunately that's probably a breaking change now.

[kevinburke1]

I guess LvlFromString exists for this use case.