"halfway a line" is a very confusing phrase

If you Google for this phrase found in the Vim documentation you'll find
almost exclusively hits from the Vim documentation. I think changing
"halfway a line" to "halfway through a line" makes more sense.

There seems to be an pervasive odd use of the word 'halfway' in the
original docs which I'm updating everywhere.

src/nvim/ex_cmds.c

@@ -3093,7 +3093,7 @@ do_ecmd (
   if (!skip_redraw) {
     n = p_so;
     if (topline == 0 && command == NULL)
-      p_so = 999;                       /* force cursor halfway the window */
+      p_so = 999;        // force cursor to be vertically centered in the window
     update_topline();
     curwin->w_scbind_pos = curwin->w_topline;
     p_so = n;