This replaces the MAX_LOGLEVEL define with a constexpr variable
in order to fix self-comparison warnings in the logging macros
when compiling with Clang. (Without this change, the log level check
in the logging macros is expanded into something like this:
`if (LINFO <= LINFO)`, which triggers a tautological compare warning.)
SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.
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.
