input: Write a python function to extract all hyperlinks from a given URL.
  assert web_crawler('https://example.com') == ['https://www.iana.org/domains/example']
  assert web_crawler('https://httpbin.org/') == ['/forms/post', '/html', '/image', '/image/png', '/image/jpeg']
  assert web_crawler('https://github.com/') == ['https://github.com/features', 'https://github.com/enterprise', 'https://github.com/team']
output: def web_crawler(url):
      import requests
      from bs4 import BeautifulSoup
      import re
  
      response = requests.get(url)
      soup = BeautifulSoup(response.content, 'html.parser')
      links = []
      for a_tag in soup.find_all('a', href=True):
          href = a_tag['href']
          if re.match(r'^https?://', href):
              links.append(href)
          elif not re.match(r'^(#|mailto:)', href):
              links.append(href)
      return links