New logger

[vyzo]

Rewrites the std/logger library for better logging, allowing per source thresholds to control verbosity.

[fare]

Can we leave some backward-compatible function log-error around? It seems to be used a lot still.

[fare]

If we're that close, shouldn't we accept the same levels as the syslog(3) facility?

Values for level
  This determines the importance of the message.  The levels are, in  order  of  decreasing  importance:
    LOG_EMERG      system is unusable
    LOG_ALERT      action must be taken immediately
    LOG_CRIT       critical conditions
    LOG_ERR        error conditions
    LOG_WARNING    warning conditions
    LOG_NOTICE     normal, but significant, condition
    LOG_INFO       informational message
    LOG_DEBUG      debug-level message

I see that on Linux, /usr/include/sys/syslog.h just imports the arch-dependent value from /usr/include/x86_64-linux-gnu/sys/syslog.h, that has:

#define LOG_EMERG       0       /* system is unusable */
#define LOG_ALERT       1       /* action must be taken immediately */
#define LOG_CRIT        2       /* critical conditions */
#define LOG_ERR         3       /* error conditions */
#define LOG_WARNING     4       /* warning conditions */
#define LOG_NOTICE      5       /* normal but significant condition */
#define LOG_INFO        6       /* informational */
#define LOG_DEBUG       7       /* debug-level messages */