use static_level_no in explicit methods

[tds333]

Small performance improvement if no logging is needed.
Also use the default static_level_no in known methods. Defaults can be used because changes are not allowed.

[Delgan]

Thanks for the improvement, @tds333!
Level severity can't be changed since #209, indeed, and I didn't realize it meant we could also early exit the function without the (somewhat expensive) getframe() call.

Actually, your PR made me realize I could also generalize this improvement to the .log() function and also remove the static_level_no argument for simplification. See a37d2d1.
It implies an additional dict lookup (error-free) compared to your solution, but I think it's totally negligible (and probably faster for the case without early exit).

[tds333]

I had the same in mind. But then decided to submit only a minimal change.
I think the refactoring improves and simplifies the code. Thanks