input: Write a python function to convert a date string in the format "Month Day, Year" to a timestamp.
  assert convert_to_timestamp("January 1, 2020") == 1577836800.0
  assert convert_to_timestamp("December 25, 1995") == 819907200.0
  assert convert_to_timestamp("July 4, 1776") == -6106017600.0
output: def convert_to_timestamp(date_string):
      from datetime import datetime
      dt = datetime.strptime(date_string, "%B %d, %Y")
      return dt.timestamp()