clogger 2.3.0 - $request_time{POWER,PRECISION} support

The $request_time can now be multiplied by a power-of-10,
allowing up to nanosecond resolution without decimals.

Thanks to Josh Natanson for contributing this feature:

https://yhbt.net/clogger-public/CAPdx2swO4eaOWaqL4-rMLq1H7pH6w-i760vPJTb92tyKfcc01Q@mail.gmail.com/
https://yhbt.net/clogger-public/CAPdx2szjqUuFjUtrgoeXXwmz0HzfdnWe+2h2Sp_ywDkTDVL0-g@mail.gmail.com/T/

There's also some minor fixes and doc updates:

  clogger: fix _BSD_SOURCE and _SVID_SOURCE deprecation warnings
  doc: update with IMAPS, NNTPS, and .onion mail archive URLs
  doc: document Fiber.current