context.cpp had grown to hold three unrelated concerns: the context
lifecycle, everything about the .conf file format, and everything about
writing a log message.
conf.cpp now owns the format end to end - parsing a file into the store,
reading values back out, and interpreting a configured string as the
boolean or log level a setting holds. logging.cpp owns the write path:
the level filter, the stream choice, and the name a level carries in
output.
context.cpp keeps what a context is: resolving each setting from the
override, the configured value, or the built-in default, and reporting
what it resolved.
