input: Write a function to convert HTML to plain text without using any libraries. If the given HTML string is empty then return an empty string.
  assert html_to_text("<p>Hello World!</p>")=="Hello World!"
  assert html_to_text("<h1>Header</h1>")=="Header"
  assert html_to_text("<ul><li>Item 1</li><li>Item 2</li></ul>")=="Item 1Item 2"
  assert html_to_text("<a href='example.com'>Link</a>")=="Link"
  assert html_to_text("")==""
output: def html_to_text(html):
      if not html:
          return ""
      text = ""
      inside_tag = False
      for char in html:
          if char == '<':
              inside_tag = True
          elif char == '>':
              inside_tag = False
          elif not inside_tag:
              text += char
      return text