Fixes several small bugs regarding #48

- Proxies are `off` by default so `SHADOWSOCKS_PASSWORD` is not required
- Documentation fixed and clarified
- `PORT_FORWARDING` should be `on` or `off` only now (although it's backward compatible with `false` and `true`)

Dockerfile

@@ -28,14 +28,14 @@ ENV USER= \
     BLOCK_NSA=off \
     UNBLOCK= \
     EXTRA_SUBNETS= \
-    PORT_FORWARDING=false \
+    PORT_FORWARDING=off \
     PORT_FORWARDING_STATUS_FILE="/forwarded_port" \
-    TINYPROXY=on \
+    TINYPROXY=off \
     TINYPROXY_LOG=Critical \
     TINYPROXY_PORT=8888 \
     TINYPROXY_USER= \
     TINYPROXY_PASSWORD= \
-    SHADOWSOCKS=on \
+    SHADOWSOCKS=off \
     SHADOWSOCKS_LOG=on \
     SHADOWSOCKS_PORT=8388 \
     SHADOWSOCKS_PASSWORD=