Guess the extension for a file based on its MIME type.
Return value is a string giving a filename extension,
including the leading dot ('.'). The extension is not
guaranteed to have been associated with any particular data
stream, but would be mapped to the MIME type 'type' by
guess_type(). If no extension can be guessed for 'type', None
is returned.
Optional 'strict' argument when false adds a bunch of commonly found,
but non-standard types.