rename LOWDATA segment to LOWBSS
Merge pull request #55 from groessler/gh-pages_to_pull

doc update: rename LOWDATA segment to LOWBSS
Rename 'syschk' symbol in the linker config file, which forces inclusion
of the 'system check' load chunki, to '__SYSTEM_CHECK__'.
Merge pull request #57 from groessler/gh-pages_to_pull

atari doc update due to cfg file changes