Missing <board>.upload.maximum_data_size=<size> entry in boards.txt

e.g. "digispark-tiny.upload.maximum_data_size=512"

This entry is necessary to show the used RAM like:
"Minimum Memory Usage: 268 bytes (52% of a 512 byte maximum)"

when compiling a sketch.

Edit: It's "board.txt" not "boards.txt"
