Biggest change is no longer using standard library's tls.Config.getCertificate function to get a certificate during TLS handshake. Implemented our own cache which can be changed dynamically at runtime, even during TLS handshakes. As such, restarts are no longer required after certificate renewals or OCSP updates.
We also allow loading multiple certificates and keys per host, even by specifying a directory (tls got a new 'load' command for that).
Renamed the letsencrypt package to https in a gradual effort to become more generic; and https is more fitting for what the package does now.
There are still some known bugs, e.g. reloading where a new certificate is required but port 80 isn't currently listening, will cause the challenge to fail. There's still plenty of cleanup to do and tests to write. It is especially confusing right now how we enable "on-demand" TLS during setup and keep track of that. But this change should basically work so far.
Before, we were activating Let's Encrypt after all the directives were executed. This means their setup functions had access to potentially erroneous information about the server's TLS setup, since the letsencrypt package makes changes to the port, etc. Now, we execute all directives up to and including tls, then activate letsencrypt, then finish with the rest of the directives. It's a bit ugly, but I do think it is more correct. It also fixes some bugs, for example: a host that only has a catch-all redirect.
Merged config and app packages into one called caddy. Abstracted away caddy startup functionality making it easier to embed Caddy in any Go application and use it as a library. Graceful restart (should) now ensure child starts properly. Now piping a gob bundle to child process so that the child can match up inherited listeners to server address. Much cleanup still to do.
