discard logging in webgo framework.

This creates a logger with output to a /dev/null equivalent. You still pay
the price for formatting and copying, but there will be no IO or write
syscalls caused by logging.

refs #253
webgo: switch off date/time formatting

This should make log discarding even faster as no date/time information
is generated.
Merge pull request #510 from nightlyone/discard_logs

discard logging in webgo framework.