Try to make the log directory if it doesn't exist

This uses @capflam's patch from https://github.com/klacke/yaws/pull/145
to create the log directory if specified like

    logdir = +path/to/log

in the configuration file.
Merge remote-tracking branch 'MrStaticVoid/yaws-1.96/try-to-create...

...-log-dir-if-specified-in-config'