v2: Implement Caddyfile enhancements (breaking changes) (#2960)

* http: path matcher: exact match by default; substring matches (#2959)

This is a breaking change.

* caddyfile: Change "matcher" directive to "@matcher" syntax (#2959)

* cmd: Assume caddyfile adapter for config files named Caddyfile

* Sub-sort handlers by path matcher length (#2959)

Caddyfile-generated subroutes have handlers, which are sorted first by
directive order (this is unchanged), but within directives we now sort
by specificity of path matcher in descending order (longest path first,
assuming that longest path is most specific).

This only applies if there is only one matcher set, and the path
matcher in that set has only one path in it. Path matchers with two or
more paths are not sorted like this; and routes with more than one
matcher set are not sorted like this either, since specificity is
difficult or impossible to infer correctly.

This is a special case, but definitely a very common one, as a lot of
routing decisions are based on paths.

* caddyfile: New 'route' directive for appearance-order handling (#2959)

* caddyfile: Make rewrite directives mutually exclusive (#2959)

This applies only to rewrites in the top-level subroute created by the
HTTP caddyfile.

cmd/main.go

@@ -134,6 +134,13 @@ func loadConfig(configFile, adapterName string) ([]byte, error) {
 		}
 	}
 
+	// as a special case, if a config file called "Caddyfile" was
+	// specified, and no adapter is specified, assume caddyfile adapter
+	// for convenience
+	if filepath.Base(configFile) == "Caddyfile" && adapterName == "" {
+		adapterName = "caddyfile"
+	}
+
 	// load config adapter
 	if adapterName != "" {
 		cfgAdapter = caddyconfig.GetAdapter(adapterName)