input: Write a function to convert an HTML string to plain text without using any libraries. The function should remove all HTML tags and return the pure text content.
  def html_to_text(html_string):
      output = ''
      in_tag = False
      for char in html_string:
          if char == '<':
              in_tag = True
          elif char == '>':
              in_tag = False
          elif in_tag == False:
              output += char
      return output
  assert html_to_text("<html><body><h1>Hello, World!</h1></body></html>")=="Hello, World!"
  assert html_to_text("<p>This is a paragraph.</p>")=="This is a paragraph."
  assert html_to_text("Hello, <b>World!</b>")=="Hello, World!"
  assert html_to_text("<title>Title</title>")==""
  assert html_to_text("")==""
output: def html_to_text(html_string):
      output = ''
      in_tag = False
      for char in html_string:
          if char == '<':
              in_tag = True
          elif char == '>':
              in_tag = False
          elif in_tag == False:
              output += char
      return output