Allow turning off logging with Level.OFF

[YarnSphere]

Fixes #310.

I added the minimum amount of code to make this work, together with a test for JS and native.

It might make sense to add an isOff property to KLogger (which could probably even be implemented in common code as !isErrorEnabled), let me know what you think.

[oshai]

the PR lgtm thanks!
Adding a method sounds good. Maybe call is isLoggingOff?

[YarnSphere]

Got it, I'll give it a go when I have a few more minutes to spare. Feel free to push to this branch if you manage to get to it before I do.

[oshai]

Thanks!
Why didn't you implement it as !isErrorEnabled in the common interface? Isn't it enough?
Sounds like a good default.

[YarnSphere]

My reasoning was that some implementations have their own notion of "off", so I thought it's better to defer to them on what they consider to be "off". Also, for consistency with the rest of the isLevelEnabled implementations.

The Android logging, for example, has the level ASSERT after ERROR, so OFF wouldn't be truly "off" due to assert logs.

JUL allows subclassing and defining custom levels between SEVERE (1000) and OFF (Integer.MAX_VALUE), I'm not sure if this would ever be supported, but in such a case this implementation would hold.

Either way, if you'd prefer it as a common implementation with a simple !isErrorEnabled let me know. Also let me know if the JVM isLoggingOff function receiving a marker makes sense or whether we should remove it.

[oshai]

Thanks! Since I am doing other changes in #320 I am going to merge this one before to avoid conflicts.

Might change some things that were discussed in previous comments later.