input: Write a python function to download the content of websites in a given list and save them as HTML files.
  assert download_websites(['http://example.com', 'http://example.org']) == ['example.html', 'example.html']
  assert download_websites(['http://test.com', 'http://demo.com']) == ['test.html', 'demo.html']
output: import requests
  
  def download_websites(url_list):
      filenames = []
      for url in url_list:
          response = requests.get(url)
          domain = url.split("//")[-1].split("/")[0].split(".")[0]
          filename = f"{domain}.html"
          with open(filename, "w", encoding='utf-8') as file:
              file.write(response.text)
          filenames.append(filename)
      return filenames