Support for rolling over log files on SIGHUP.

This first commit just handles "fast" logs for now.
Rollover json (eve) log on SIGHUP.
Add macros for access to the underlying buffer and offset.
Check for rollover in the default Write function.
Add signal based rotation to http-log.
Signal based file rotation for dns-log.
Signal based file rotation for tls log.
Pass the write through to the LogFileCtx, it will handle rollover.
Move the rotation notification to the main loop.  Only a flag
is set in the signal handler now.