Add more keys to remap

I just discovered this mode.  I had similar settings in my emacs init.  I would like to also change the keys for the up & down arrows to follow the up and down behavior, and the left and right keys to cycle through the history or do the ido-next-match-dir.  It basically switches the up and down and left and right keys.
Made this customizable...

Note that you are overwriting =ido-toggle-prefix= with =C-p=.
Added ido-toggle-prefix back to ido-vertical-mode
logic fix for installing keys.
Use ido-vertical prefix instead of sd/
Introduce cask and ert-runner to ido-vertical-mode
Add docstrings for defvars
Remove redundancy in names brought about by e2d6e8f
Prevent `ido-vertical-mode' from overwriting its own 'old' vars
Reorganize defgroup and define-minor-mode
Update docstrings for next/prev-match
Update readme to reflect options from #4
Update meta information
Use more straightforward method for invoking ido in tests