Set up to level

[franciscocpg]

level.SetUpToLevel creates the possibility to set a log level that is enabled up to the desired level.
This way, one can create different formatters for low levels and high levels.
For example:

    format1 := MustStringFormatter("%{color}%{time:15:04:05.000} %{level:.4s} %{id:03x} %{message}%{color:reset}")
    backend1 := NewLogBackend(os.Stderr, "", 0)
    backendFormatter1 := NewBackendFormatter(backend1, format1)
    backendLeveled1 := AddModuleLevel(backendFormatter1)
    backendLeveled1.SetUpToLevel(INFO, "")

    format2 := MustStringFormatter("%{color}%{time:15:04:05.000} %{longfile}:%{shortpkg}.%{longfunc} ▶ %{level:.4s} %{id:03x} %{message}%{color:reset}")
    backend2 := NewLogBackend(os.Stderr, "", 0)
    backendFormatter2 := NewBackendFormatter(backend2, format2)
    backendLeveled2 := AddModuleLevel(backendFormatter2)
    backendLeveled2.SetLevel(ERROR, "")
    SetBackend(backendLeveled1, backendLeveled2)
    log := MustGetLogger("testing")
    log.Debug("debug")
    log.Info("info")
    log.Error("error")

will result in a format for levels up to INFO and another for ERROR or CRITICAL.

[op]

Wouldn't it make more sense to add a SetMaxLevel function and track these levels separately? Please add tests.

[op]

I also can't guarantee that I will merge this. It feels like there has to be a cleaner approach.

[op]

Sorry for the delay. Wouldn't it be nicer if you created a new backend which adds this functionality? Closing for now. Please open a new PR where you haven't disabled tests.