Inconsistent API

[anacrolix]

• SetLogLevel has a special case for *, yet SetAllLoggers exists.
• SetLogLevel takes level as a string, instead of a "github.com/whyrusleeping/go-logging".Level.

[iand]

I believe both of these inconsistencies are to for backwards compatible support for existing clients of the package

[Kubuxu]

There is still quite a way until we update everything to v2.
Maybe we should look at doing major cleanup as v3 and update to it too.