Bind Ctrl+MouseWheel to scroll up/down

On my system, Shift+Mouse is captured by the terminal and
Alt+Mouse only works for one of the alt keys. Hence I picked
Ctrl.

This also allows binding of Ctrl+MouseButtons (but doesn't set
any such bindings). That should also allow usign Ctrl+Click to
select `lf`'s terminal without moving the cursor no matter
where you click.  On tmux, this doesn't work out of the box and
requires a change to `tmux.conf` along the following lines:

     bind-key -T root  C-MouseDown1Pane  select-pane -t = \; send-keys -M

doc.go

@@ -226,7 +226,7 @@ If the 'mouse' option is enabled, mouse buttons have the following default effec
 	    Enter a directory or open a file. Also works on the preview window.
 
 	Scroll wheel
-	    Scroll up or down.
+	    Move up or down. If Ctrl is pressed, scroll up or down.
 
 # Configuration
 

lf.1

@@ -259,7 +259,7 @@ If the 'mouse' option is enabled, mouse buttons have the following default effec
 .PP
 .EX
     Scroll wheel
-        Scroll up or down.
+        Move up or down. If Ctrl is pressed, scroll up or down.
 .EE
 .SH CONFIGURATION
 Configuration files should be located at:

opts.go

@@ -139,13 +139,15 @@ func init() {
 	gOpts.keys["<c-b>"] = &callExpr{"page-up", nil, 1}
 	gOpts.keys["<pgup>"] = &callExpr{"page-up", nil, 1}
 	gOpts.keys["<c-y>"] = &callExpr{"scroll-up", nil, 1}
+	gOpts.keys["<c-m-up>"] = &callExpr{"scroll-up", nil, 1}
 	gOpts.keys["j"] = &callExpr{"down", nil, 1}
 	gOpts.keys["<down>"] = &callExpr{"down", nil, 1}
 	gOpts.keys["<m-down>"] = &callExpr{"down", nil, 1}
 	gOpts.keys["<c-d>"] = &callExpr{"half-down", nil, 1}
 	gOpts.keys["<c-f>"] = &callExpr{"page-down", nil, 1}
 	gOpts.keys["<pgdn>"] = &callExpr{"page-down", nil, 1}
 	gOpts.keys["<c-e>"] = &callExpr{"scroll-down", nil, 1}
+	gOpts.keys["<c-m-down>"] = &callExpr{"scroll-down", nil, 1}
 	gOpts.keys["h"] = &callExpr{"updir", nil, 1}
 	gOpts.keys["<left>"] = &callExpr{"updir", nil, 1}
 	gOpts.keys["l"] = &callExpr{"open", nil, 1}

ui.go

@@ -1189,12 +1189,18 @@ func (ui *ui) readNormalEvent(ev tcell.Event, nav *nav) expr {
 		case tcell.ButtonNone:
 			return nil
 		}
+		if tev.Modifiers() == tcell.ModCtrl {
+			button = "<c-" + button[1:]
+		}
 		if expr, ok := gOpts.keys[button]; ok {
 			return expr
 		}
-
-		if tev.Buttons() != tcell.Button1 && tev.Buttons() != tcell.Button2 {
-			return nil
+		if tev.Modifiers() == tcell.ModCtrl || (tev.Buttons() != tcell.Button1 && tev.Buttons() != tcell.Button2) {
+			ui.echoerrf("unknown mapping: %s", button)
+			ui.keyAcc = nil
+			ui.keyCount = nil
+			ui.menuBuf = nil
+			return draw
 		}
 
 		x, y := tev.Position()