Provides a basic extension to the interface to begin migration off of
the printf-based logging system.
Everything will go through macros with the same style naming as the old
logging system, except the macros will have the _FMT suffix, while the
migration is in process.
This allows for peacemeal migration over time instead of pulling
everything out and replacing it all in a single pull request, which
makes for much easier reviewing.
Previously the logging was a in a little bit of a disarray. Some things
were in namespaces, and other things were not.
Given this code will feature a bit of restructuring during the
transition over to fmt, this is a good time to unify it under a single
namespace and also remove functions and types from the global namespace.
Now, all functions and types are under the Common::Log namespace. The
only outliers being, of course, the preprocessor macros.
