added comment operator (similarly to the delete/change operator) 

Modified evil-delete to create evilnc-comment-operator.  Takes a motion or text object and comments it.  Also yanks content in the process.

This should resolve the evil parts of #11 and #8.  It also allows for massive simplification of the evil keybindings:

    (define-key evil-normal-state-map "," 'evilnc-comment-operator)
    (define-key evil-visual-state-map "," 'evilnc-comment-operator)

since the previous functionality can be done via text objects/motions (see updated readme for details).

Known bugs:

1. If you try to uncomment a subregion of a commented line, that subregion gets double-commented while the portions ahead of it get uncommented.