Various fixes/tweaks to HTTP placeholder variables and file matching

- Rename http.var.* -> http.vars.* to be more consistent
- Prefixing a path matcher with * now invokes simple suffix matching
- Handlers and matchers that need a root path default to {http.vars.root}
- Clean replacer output on the file matcher's file selection suffix

modules/caddyhttp/fileserver/staticfiles.go

@@ -57,6 +57,10 @@ func (FileServer) CaddyModule() caddy.ModuleInfo {
 
 // Provision sets up the static files responder.
 func (fsrv *FileServer) Provision(ctx caddy.Context) error {
+	if fsrv.Root == "" {
+		fsrv.Root = "{http.vars.root}"
+	}
+
 	if fsrv.IndexNames == nil {
 		fsrv.IndexNames = defaultIndexNames
 	}