input: Write a function to convert HTML to plain text without using any libraries. The function should take an HTML string as input and return the plain text version of the string by removing all HTML tags. If the input string is empty, the function should return an empty string.
  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("<p>Hello, <b>world</b>!</p>") == "Hello, world!"
  assert html_to_text("<h1>Title</h1><p>Paragraph</p>") == "TitleParagraph"
  assert html_to_text("<a href='#'>Link</a>") == "Link"
  assert html_to_text("No HTML here") == "No HTML here"
  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