OSWORD 0 improvements

[tom-seddon]

OSWORD 0 has always been rubbish. How about some better editing facilities? The cursor keys are already booked for entering copy mode - but there are options!

Some random thoughts:

• Can always fall back to the old mode if there are any obvious problem cases, and you're no worse off...
• Handling tiny text windows would get complicated, but it's probably detectable. YOu'll need to handle some of these cases ordinarily anyway
• Would the various text direction modes present a problem?
• Meta+letter keys would be a viable alternative to cursor keys. Ctrl+U (erase input) is already a thing, so there's a precedent
• VDU 5 will make a big mess, though it isn't exactly great with the existing code
• If using meta keys to move insert cursor - check soft key modes and fall back to old mode if the keypresses of interest are actually soft keys
• Pick up unused regions in HAZEL and use those as a history buffer?