To override it a board must define MICROPY_BOARD_FATAL_ERROR to a function
that takes a string message and does not return.
Signed-off-by: Damien George <damien@micropython.org>
Previously the end of the heap was the start (lowest address) of the stack.
With the changes in this commit these addresses are now independent,
allowing a board to place the heap and stack in separate locations.
This is to keep the top-level directory clean, to make it clear what is
core and what is a port, and to allow the repository to grow with new ports
in a sustainable way.
