New simple implementation for YAML serialization

Tiny in size so we don't need to fetch the 80KB yaml package for simple
YAML serializaiton needs in various pages. It's also 8x faster than
yaml package so that's a big plus for debug logging.

test/yaml.ts

@@ -0,0 +1,14 @@
+import ava from "ava";
+import * as yaml from "yaml";
+import { stringify } from "../lib/common/yaml";
+
+import testCases from "./yaml-tests.json";
+
+ava("stringify", (t) => {
+  for (const testCase of testCases) {
+    let str = stringify(testCase);
+    if (str.startsWith(">2")) str = ">3" + str.slice(2);
+    if (str.startsWith("|2")) str = "|3" + str.slice(2);
+    t.deepEqual(yaml.parse(yaml.stringify(testCase)), yaml.parse(str));
+  }
+});