lws access log option and lwsws conf

This adds the ability to store apache-compatible logs to a file given at
vhost-creation time.

lwsws conf can set it per-vhost using "access-log": "<filepath>"

The feature defaults to disabled at cmake, it can be set independently but
LWS_WITH_LWSWS set it on.

Signed-off-by: Andy Green <andy@warmcat.com>