* Change Mock API to match mockNetConn Expect* calls.
* Make logging.NewMock take and store *testing.T.
* Add a level-agnostic Expect().
* Make writerMap an externally accessible type.
* Adjust tests to take this shaving into account.
1) Adjust alignments for exp/got correctly.
2) Print expected string when nothing logged at level.
3) Check to ensure no unexpected logging occurred at other levels when nothing
logged at expected level.
Allowing people to use the static functions to log things makes testing
hard, so I've removed them. I've also rewritten things to allow logging
different levels to separate files.
