Prompt user for input and fix evilnc-kill-to-line

Prompt user input for following commands:

- evilnc-comment-or-uncomment-to-the-line
- evilnc-copy-to-line
- evilnc-copy-and-comment-lines
- evilnc-kill-to-line

If a prefix argument is supplied, then prompt won't appear.

Also fix evilnc-kill-to-the-line error when the extra newline at end of
file does not exist. For example, if line 8 is the last line and no
newline at the end, then kill to line 8 causes this error like this:

    Args out of range: #<buffer *scratch*>, 192, 212

This PR is to fix this issue: https://github.com/redguardtoo/evil-nerd-commenter/issues/31