Upgrade to kaya 0.0.2 and run on the rloop event loop

- pin kaya-core/kaya-rsgi >= 0.0.2 (ctx.client now honors Forwarded and
  X-Forwarded-* headers); adapt route tests and add explicit coverage
- add rloop dependency and set GRANIAN_LOOP=rloop in the Docker image so
  granian serves the app on the Rust event loop instead of asyncio
- regenerate requirements.txt (kaya 0.0.2, rloop 0.5.0)
- document the new loop and forwarded-header behavior in the README

Dockerfile

@@ -40,7 +40,8 @@ ENV PATH="/opt/venv/bin:$PATH" \
     PYTHONDONTWRITEBYTECODE=1 \
     GRANIAN_HOST=0.0.0.0 \
     GRANIAN_PORT=8080 \
-    GRANIAN_INTERFACE=rsgi
+    GRANIAN_INTERFACE=rsgi \
+    GRANIAN_LOOP=rloop
 
 USER app