Face for literal numbers.

[Ergus]

Hi I have seen that vim provides a color for the literal numbers in
prog-modes. I was looking for something similar en emacs and
surprisingly there is nothing within emacs or at least in elpa. The only
similar (fully functional) package is in melpa:

https://github.com/Fanael/highlight-numbers

Could we provide some basic support for this without depending of
melpa. Such simple functionalities must be at least in elpa right?