Taking inspiration from acme-client.

also, while here, add some error checking too

replace its only usage with strncmp(). it's likely faster too.

this revamps the syntax in the configuration to better match httpd(8) (and in general be less weird) and to allow per-location fastcgi configurations. the bare `param' is now deprecated, but for compatibility it acts like `fastcgi param' would do now. Same story for `fastcgi <pathÂ>'.

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 dup(1) the ca fd and send it to various processes, so they fail loading it. Instead, use load_file to get a buffer with the file content and pass that to load_ca which then loads via BIO.

Incorporate the OpenSMTPD' privsep crypto engine. The idea behind it is to never load the certificate' private keys in a networked process, instead they are loaded in a separate process (the `crypto' one) which signs payloads on the behalf of the server processes. This way, we greatly reduce the risk of leaking the certificate' private key should the server process be compromised. This currently compiles only on LibreSSL (portable fix is in the way).

Was temporarly disabled during the transition to real privsep. While here, fix a memory leak when using `require client ca'. Also, avoid leaking info about the parent address space layout to server processes by not sending pointer values.