input: Write a python function to get all links from a given URL using HTMLParser.
  assert len(get_all_links("http://www.website.com")) > 0
  assert isinstance(get_all_links("http://www.website.com"), list)
output: from html.parser import HTMLParser
  import urllib.request
  
  class LinkParser(HTMLParser):
      def __init__(self):
          super().__init__()
          self.links = []
  
      def handle_starttag(self, tag, attrs):
          if tag == 'a':
              for attr in attrs:
                  if attr[0] == 'href':
                      self.links.append(attr[1])
  
  def get_all_links(url):
      response = urllib.request.urlopen(url)
      html = response.read().decode()
      parser = LinkParser()
      parser.feed(html)
      return parser.links