Shadowing core "I" is too messy. As soon as ed is loaded in memory,
nothing else that isn't "i-aware" can be loaded anymore.
I guess that's why "contexts" exist in Starting Forth, but adding
this concept just for allowing the shadowing of core words seems
overkill to me. Renaming I to i in ed seems better.
Make F search from curpos+1 so that it's possible to search the
same word we've just found a second time. Previously, it would find
the word under the cursor.
Also, improve docs a bit.
Also, made LIST properly handle full 64-chars lines not ending with
a null or CR. Previously, such a line would be accompanied by its
following line, duplicating that line's output.
