1.1.0: Memory and file more for Python reader

• The pure Python reader now supports an optional file and memory mode in
  addition to the existing memory-map mode. If your Python does not provide
  the mmap module, the file mode will be used by default.
• The preferred method for opening a database is now the open_database
  function in maxminddb. This function now takes an optional read
  mode.
• The C extension no longer creates its own InvalidDatabaseError class
  and instead uses the one defined in maxminddb.errors.