[Suggestion] add support for shift selections (marking) for some puni operations

[Inc0n]

(interactive "^") allow a command to be marking if the keybind of that command is activated with a shift key pressed, if shift-select-mode is activated.

So as of now, C-M-S-f (puni-forward-sexp) would not mark anything but to move cursor a sexp worth forward.
This addition would allow the region to be marked also, this can be convenient feature to be added in.

The puni commands that could benefit from this, I would think:

• puni-forward-sexp
• puni-backward-sexp
• puni-end-of-sexp
• puni-beginning-of-sexp

[AmaiKinono]

Close by #37.