It now figures out the file type from the file extension. If no file
extension is given it just saves the file as BMP if its not a JPEG image
or JPEG if it's a JPEG image. If you specify an extension and the file is
not of that type then it will give you an error.
The new test_save.py should run until you reach the JPEG image part
where it quits due to lack of JPEG support natively on OV7725 boards.
Maybe JPEG mode should be supoorted by just compressing pictures?