refactor REDIRECT_PROTO and add some examples

examples/phpinfo-behind-https/Caddyfile

@@ -0,0 +1,7 @@
+https://* {
+    errors stderr
+    tls self_signed
+    proxy / http://backend:80 {
+        transparent
+    }
+}

examples/phpinfo-behind-https/docker-compose.yml

@@ -0,0 +1,13 @@
+version: '3'
+services:
+    backend:
+        build: ../../
+        volumes:
+        - './index.php:/var/www/index.php'
+
+    frontend:
+        image: abiosoft/caddy
+        volumes:
+        - './Caddyfile:/etc/Caddyfile'
+        ports:
+        - '443:443'

examples/phpinfo-behind-https/index.php

@@ -0,0 +1,3 @@
+<?php
+
+phpinfo();