Back to characters, direct updates.

Should make it a bit faster, not having to map and map again; thought
the cost is very minimal.
Removing dead code
Umm...

So this ended up being much faster (like, the screen actually keeps up
with a held-down key) even though I didn't really do it to increase
performance.
Colors!

Now there are two table lookups for the character and the color -- I
might try to squeeze these back into one lookup.

Did I mention that I hate data entry?
Double-sized blocks and single-time lookup;

All the speed, none of the drawbacks.  And it should be easier to find
one's way around, since the blocks will actually be a block on most
screens.
Added new entity "LargeFern" according to observation.