Delete Message Files and Replies

• add a new .files field to SlackMessage containing all the files attached to the message
• add new options to SlackMessage.delete files=True will also delete attached files, replies=True does the same thing for the replies aka. thread.

Thus, deleting everything possible should be reduced to:

s = SlackCleaner2(TOKEN)
for msg in s.msgs():
  msg.delete(files=True, replies=True)