fserv v0.18

+ http: added source code for modules: http, errdoc, static-file, dir-index, status, gzip
+ log: support logging while reading configuration on server start
+ net.listen: config: max_clients option for each listener
- connect: fix crash when using keep-alive connections cache
- connect: fix crash when using debug logging
- resolve: IPv4/v6 resources stored in cache didn't work in some cases
- log: correctly add new-line after a large message
- log: error messages were printed to stdout instead of stderr
* core: process_vars() uses ffstr3