Make Yi.Core less kitchen-sinky.
Use newlineB
Don't try to indent backwards

This happened when we went back 1 character in eolPoint to make it look
to the user like we're at the end of the current line rather than ending
up at beginning of the next one.

Fixes #621
Get rid of *RegionClever

Considering the need for conversion into String and number of operations
done by the result, it's Probably™ just faster to replace the whole region.