add --caption option to set window title
add coord_ok docstring
add --text-width mode for initial width (40 for pcjr, cga; 80 otherwise)
on pcjr: cls, and cls number give syntax error. on tandy: cls number gives illegal function call; cls, is ok
HELP: typo
WIDTH: don't allow unbracketed numeric calculations; bring errors closer in line with GW-BASIC
limit keyboard buffer to 15 chars, then beep; exceptions: text, cli interfaces, pasting and inserting keys at startup
add video memory size option --video-memory
tandy/pcjr: set number of pages based on available video memory.
determine ega number of pages based on video memory size
implement code-memory address PEEKs
implement keyboard low-memory PEEKs
re-implement keybuf to emulate ring buffer
rename get_font_memory -> get_rom_memory
implement more low memory PEEKs
for (strict) protected programs, disallow CHAIN MERGE; POKE, PEEK, BLOAD and BSAVE in direct mode
allow setting program protection flag with DEF SEG:POKE 1450,n
do not crash on loading empty ascii files