Merge pull request #36 from mccutchen/https-or-not

Allow serving non-index pages via plain HTTP (fixes #35)

app.yaml

 ---
-runtime: go112
+runtime: go113
 
 main: ./cmd/go_httpbin
 
-# redirect everything to https
 handlers:
-  - url: /.*
+  # Always redirect index requests to https
+  - url: /
     script: auto
     secure: always
     redirect_http_response_code: 301
+
+  # Allow requests for any other resources via either http or https
+  - url: /.+
+    script: auto
+    secure: optional