Extract the revisions of a page.

  Args:
    page: a string
  Returns:
    a list of strings

def get_revisions(page):
  """Extract the revisions of a page.

  Args:
    page: a string
  Returns:
    a list of strings
  """
  start_string = "    <revision>\n"
  end_string = "    </revision>\n"
  ret = []
  current_pos = 0
  while True:
    start_pos = page.find(start_string, current_pos)
    if start_pos == -1:
      break
    end_pos = page.find(end_string, start_pos)
    assert end_pos != -1
    ret.append(page[start_pos + len(start_string):end_pos])
    current_pos = end_pos + len(end_string)
  return ret