Implement line number in the mode line and associated logic.
Inspired by OpenBSD mg.

Requested by Pito on the RetroBSD forums.

This works in all situations except searching for strings. But can be reset by doing M-G or M-< or M->.

Implement a prompted go to line function, bound to M-G.

Remove lesser used and expensive movement functions. All movement functions are more expensive now with the line number logic. M-G can be used for quick movement around documents.

Finally, some minor formatting tweaks.