add ed0.py, editor core extracted from ed.py
ed0.py: fill in with functions moved out of ed.py
not complete, some functions not yet working in ed.py or ed0.py
ed.py revised to work with new ed0.py
tweak test_cmd.py so it works with revised ed.py and ed0.py
ed.py: continue revisions to work with new ed0.py
now shorter and neater, but revised a(ppend) and i(nsert) not working
ed.py: working with new ed0.py
fix bugs, add .log files to record successful test_ed*.py output
ed.py: fix extra blank line after appended text
fix sample_read.sh test script, add missing q command
ed.py: fix typo in l(), o() + 1 not 11
also revise test_ed.py and make new test_ed.log
merge ed0 branch back into master