Provide feedback from flash_loader

[maccasoft]

As of now, there is no feedback from the flash_loader stub, if something goes wrong, the user has no clue about what to fix. There isn't even a clue when the flash programming is finished, I guess it is quick but a small hint would be good.
Please provide some feedback through a simple result code if the checksum fails, or the flash programming failed, and if everything is good.

[ChipGracey]

This is a great idea. I can add a little message that will be sent upon successful completion of flash programming. Thanks. Sorry I'm so late. Just learning how all this git stuff works.