You’re using quite an old version! Please update to the latest, Caddy v2.0.0 stable was just released yesterday!
When using regexp matchers, you need to specify a name for the matcher to reference its results later. E.g. path_regexp master ^\/master\/(?P<more>.*)?$ then later, {http.regexp.master.more}.
Yes, Caddy will follow symlinks, it’s just doing regular system calls, and symlinks are handled at the system level, not the application level.