logger: make notice precede info
logger: make prefix an argument to the use method
logger: actually return self from use and use!
logger: add respond_to_missing? method
errors: add new file containing gem's exceptions
injectedlogger: add InjectedLogger.inject method

This allows users to set up a logger method that falls back to
a setup block when no logger has been use()'d and then redefines
itself so that there is no performance overhead.
README: add some more basic usage info
injectedlogger: release 0.0.3