Various bug fixes and minor improvements

- Fix static responder so it doesn't replace its own headers config,
  and instead replaces the actual response header values
- caddyhttp.ResponseRecorder type optionally buffers response
- Add interface guards to ensure regexp matchers get provisioned
- Use default HTTP port if one is not explicitly set
- Encode middleware writes status code 200 if not written upstream
- Templates and markdown only try to execute on text responses
- Static file server sets Content-Type based on file extension only
  (this whole thing -- MIME sniffing, etc -- needs more configurability)

modules/caddyhttp/fileserver/browse.go

@@ -66,6 +66,7 @@ func (fsrv *FileServer) serveBrowse(dirPath string, w http.ResponseWriter, r *ht
 		}
 		w.Header().Set("Content-Type", "text/html; charset=utf-8")
 	}
+
 	buf.WriteTo(w)
 
 	return nil