This pull requests adds a new type of external app to the firmware: The standalone app.
Pros:
Will work after an upgrade.
Size of image is only limited by shared heap size of M0 (application) (64kb total).
Cons:
No full access to all functions in the main firmware. One well defined (and versioned) API handles all communication.
The Pacman app was converted to be the first the the new kind.
* Pad image to 1MB and add simple checksum
* Test code to verify firmware checksum
* Comment out unneeded zlib
* Add files via upload
* Print space remaining in ROM
* Append checksum to external apps too
* Check external app checksums when loading
* Is it 2024 already?!
* Validate firmware checksum before flashing
* Add files via upload
* Added flash error warning to nav screen
* Clang
* Replaced some hard-coded values with #defines
* Check FW checksum before USB serial flash too
* Add files via upload
