comment and formatting fixes
rename LOWDATA segment to LOWBSS
Merge pull request #54 from groessler/something_to_pull

some cleanups for 'atarixl'
Rename 'syschk' symbol in the linker config file, which forces inclusion
of the 'system check' load chunki, to '__SYSTEM_CHECK__'.
atari-asm.cfg linker config file
Put EXE header and main chunk load header into a single file --
it makes no sense to be able to include/exclude them separately.
Merge pull request #56 from groessler/something_to_pull

atari-asm.cfg
Force inclusion of 'shadow RAM preparation' load chunk in crt0.s and
not in the linker config file.
Merge pull request #58 from groessler/something_to_pull

another small atarixl change