API change: autoflush (log) now on by default + unit tests + POD

The new autoflush feature of Catalyst::Log now defaults to true and is
left on. In order to access the old behavior, modules such as
Static::Simple must manually turn it off (i.e. by hooking
setup_finalize, see example in POD).

Also updated logger unit tests, and added a new set of
autoflush-specific tests.

Note: this API change was suggested by mst