Makefile - opt prevent data/eeprom overflow

Data and eeprom overflow is now warned about and optionally prevents
upload.
Fix shell script execution.
Merge pull request #272 from jediunix/makefile-check-data-eeprom

Makefile - opt prevent data/eeprom overflow
Merge pull request #274 from jediunix/fix-shell-scripts

Fix shell script execution.
Refactor byte swap; add unsigned data handling. Remove explicit cast.