flow.log: Alias for log::Sev::S_NONE: log::OFF.

[ygoldfeld]

Filed by @ygoldfeld pre-open-source:

(colleague) asked for a stylistic-in-nature addition to flow.log: A constant named something like OFF which can be used to set a log-level to S_NONE, thus disabling all logging in that context (whether per component or globally or...). I guess Sev::S_NONE is arguably less expressive.

If so then an extern flow::log::Sev OFF = flow::log::Sev::S_NONE would perhaps get it done while following the Coding (style) Guide too (global => no S_ prefix). Counterpoint is perhaps it's too general and should be NO_LOGGING or something. Then again flow.log is not so huge, and OFF seems okay since it would be in that namespace.