fix: Better compatibility with Express 5 by removing router dependency

Remove `router` dependency and mark `express` as peer dependency. This
way we get rid of the security warnings when we npm install this
package. We also allow the use of the Router that comes with whatever
express version the host application has.

Author: enov

package.json

@@ -20,6 +20,15 @@
     "prepublishOnly": "EXPRESS_MAJOR=4 mocha && EXPRESS_MAJOR=5 mocha",
     "postpublish": "git push origin && git push origin --tags"
   },
+  "peerDependencies": {
+    "express": ">= 4.17.0 < 6.0.0"
+  },
+  "peerDependenciesMeta": {
+    "express": {
+      "optional": true,
+      "meta": "This package imports `router`, which comes with `express`."
+    }
+  },
   "devDependencies": {
     "express": "^4.18.2",
     "express4": "github:expressjs/express#4.19.2",
@@ -34,7 +43,6 @@
     "ajv-keywords": "^5.1.0",
     "http-errors": "^2.0.0",
     "path-to-regexp": "^6.2.1",
-    "router": "^1.3.8",
     "serve-static": "^1.15.0",
     "swagger-parser": "^10.0.3",
     "swagger-ui-dist": "^5.11.8",