Transpose chars with "xp"

[herbertjones]

"x" and "X" should insert the removed character into the paste buffer.

Address #19.

[oscarfv]

With this change things like 4x seems not to work anymore. Tested with up to date Evil and Emacs 28.

[oscarfv]

Using evil-forward-char/evil-backward-char for :motion instead of nil seems to do the trick.