Add in drone configuration with basic testing

.drone.yml

@@ -0,0 +1,17 @@
+kind: pipeline
+name: tests
+
+steps:
+    # Tests ordered from quickest to slowest so failed builds fail quickly
+  - name: minimum-test
+    image: rust:1
+    commands:
+      - cargo test --no-default-features --features scgi_srv
+  - name: scgi-test
+    image: rust:1
+    commands:
+      - cargo test --no-default-features --features scgi_srv,user_management_advanced,user_management_routes,serve_dir,ratelimiting
+  - name: gemini-test
+    image: rust:1
+    commands:
+      - cargo test --features user_management_advanced,user_management_routes,serve_dir,ratelimiting