[doclint] Implement simple markdown preprocessor

This patch implements simple markdown preprocessor. The goal
is to generate certain parts of markdown, such as:
- puppeteer version
- chromium revision
- table-of-contents
- copy/paste parts of documentation (for shortcut methods)

package.json

@@ -11,7 +11,7 @@
     "unit": "jasmine test/test.js",
     "debug-unit": "DEBUG_TEST=true node --inspect-brk ./node_modules/.bin/jasmine test/test.js",
     "test-phantom": "python third_party/phantomjs/test/run-tests.py",
-    "test-doclint": "jasmine utils/doclint/check_public_api/test/test.js",
+    "test-doclint": "jasmine utils/doclint/check_public_api/test/test.js && jasmine utils/doclint/preprocessor/test.js",
     "test": "npm run lint --silent && npm run coverage && npm run test-phantom && npm run test-doclint",
     "install": "node install.js",
     "lint": "([ \"$CI\" = true ] && eslint --quiet -f codeframe . || eslint .) && npm run doc",