Log::Message is a generic message storage mechanism. It allows you to store
messages on a stack -- either shared or private -- and assign meta-data to it.
Some meta-data will automatically be added for you, like a timestamp and a
stack trace, but some can be filled in by the user, like a tag by which to
identify it or group it, and a level at which to handle the message (for
example, log it, or die with it)