Response assertion function for unit testing

• Bumps Deno to v0.23.0
• Adds response assertion function for unit testing:

import { jsonResponse, assertResponsesMatch } from "https://raw.githubusercontent.com/jamesseanwright/reno/v0.4.0/reno/mod.ts";

test({
  name: "ronSwansonQuoteHandler should fetch a quote from an API and return it",
  async fn() {
    // [...]
    const response = await ronSwansonQuoteHandler(req);

    /* Will deeply compare headers and
     * convert body bytes to strings */
    assertResponsesMatch(response, jsonResponse(quotes, {
      "X-Foo": "bar"
    }));
  }
});