This README describes the use of fxl logging in this library, and in
particular the conventions regarding verbosity levels.

When debugging an app, generally I want --verbose=1 to only contain messages
from the app. If it also contains messages from various libraries the S/N
ratio suffers enough to be painful. There is still value in having two levels
of logging: minimal and super-verbose. [There's also value in having
super-super-verbose, but that's a separate discussion.]
So if we split up app-x-lib vs minimal-x-super-verbose we get four levels:

           minimal  super-verbose
app           1          3
app+lib       2          4

This convention is employed in this library, and is intended to be
employed by the apps that use it.