Update null log handling for py26

Python 2.6 does not have a NullHandler in the logging
module, so introduce a little class that does the same
work.

Also add __all__ to the package init so extra names are
not exported.

Resolves issue #2

Change-Id: Id59d394cd02372e2c31de336894f06653cb1e22d
Merge pull request #26 from dhellmann/bug/logging-py26

Update null log handling for py26