adding api-demo to 388b code_examples

cmsc388b/code_examples/api-demo/.gitignore

cmsc388b/code_examples/api-demo/app.js

cmsc388b/code_examples/api-demo/bin/www

cmsc388b/code_examples/api-demo/models/book.js

cmsc388b/code_examples/api-demo/package-lock.json

cmsc388b/code_examples/api-demo/package.json

cmsc388b/code_examples/api-demo/public/index.html

cmsc388b/code_examples/api-demo/public/stylesheets/style.css

cmsc388b/code_examples/api-demo/routes/api/books.js

cmsc388b/code_examples/api-demo/routes/index.js

cmsc388b/code_examples/api-demo/routes/users.js