Work on #395.  Introduce a TempVisualMode.  It doesn't actually work
yet.
Fix #395.  Add support for '(insert) VISUAL' mode which returns to
InsertMode after performing a visual operation.
Update unstable update site.
Keep cursor near selection end on visual mode exit

Vim will keep the cursor in the very same spot when exiting visual mode
whereas Vrapper would always reset the selection to the top- and
left-most point of the selection.

Try to reset the pointer to a point nearest the end of the selection,
accounting for reverse selections.

Note that this isn't correct for visual line-wise mode as the caret
can only be drawn at the end of a selection.