Add half-page-{up,down} actions (#784)

src/options.go

@@ -688,6 +688,10 @@ func parseKeymap(keymap map[int]actionType, execmap map[int]string, str string)
 			keymap[key] = actPageUp
 		case "page-down":
 			keymap[key] = actPageDown
+		case "half-page-up":
+			keymap[key] = actHalfPageUp
+		case "half-page-down":
+			keymap[key] = actHalfPageDown
 		case "previous-history":
 			keymap[key] = actPreviousHistory
 		case "next-history":

src/terminal.go

@@ -186,6 +186,8 @@ const (
 	actUp
 	actPageUp
 	actPageDown
+	actHalfPageUp
+	actHalfPageDown
 	actJump
 	actJumpAccept
 	actPrintQuery
@@ -1478,6 +1480,12 @@ func (t *Terminal) Loop() {
 			case actPageDown:
 				t.vmove(-(t.maxItems() - 1))
 				req(reqList)
+			case actHalfPageUp:
+				t.vmove(t.maxItems() / 2)
+				req(reqList)
+			case actHalfPageDown:
+				t.vmove(-(t.maxItems() / 2))
+				req(reqList)
 			case actJump:
 				t.jumping = jumpEnabled
 				req(reqJump)