now common is no longer a reserved keyword

See Codeberg issue #1.

Call the certificates .pem and the keys .key; use contrib/gencert to generate the certificates and provide a GENCERT_FLAGS knob so that regress can be run with EC keys (GENCERT_FLAGS=-e). Still no automatic way of testing with both RSA and EC keys.

add `log style <style>'; The old default is called `legacy' now, a new default format is added called `condensed', and `common' and `combined' to mimick Apache httpd and nginx (respectively) are also added.

some CI envs don't like `listen on localhost' but tolerate INADDR_ANY or IN6ADDR_ANY_INIT.

Listening by default on all the addresses is so bad I don't know why I haven't changed this before. Anyway. Add a `listen on $hostname port $port' syntax to the config file and deprecate the old "port" and "ipv6" global setting. Still try to honour them when no "listen on" directive is used for backward compatibily, but this will go away in the next next version hopefully. At the moment the `listen on' in server context don't filter the host, i.e. one can still reach a host from a address not specified in the corresponding `liste on', this will be added later.

we can use cmp to tell if two files are different, which also has the benefit of being available everywhere and reporting the byte offset of the first difference. Reduces the test dependencies on some systems.