update to use tiddlyweb 1.4.2 logging style

That style configures logging handlers for the 'tiddlyweb'
and 'tiddlywebplugins' namespaces. These can then be accessed
with a getLogger in plugin code.
Merge pull request #4 from cdent/tiddlyweb1.4.2

update to use tiddlyweb 1.4.2 logging style