Improved the nocompatible comment.

Now it actually describes what I'm pretty sure it's for.
Added nrformats= which limits number editing

Usually it will edit numbers by context. So it it will increment and
decrement 004 as an octal number. This setting makes vim treat all
numbers as decimal.
Added vim-commentary by tpope.

Also removed my old commenting bundle by scrooloose. The tpope one seems
a bit better.