Add stackundo option

cmd/micro/eventhandler.go

@@ -118,6 +118,10 @@ func (eh *EventHandler) Undo() {
 		undoThreshold := int64(settings["undothreshold"].(float64))
 		if startTime-(te.time.UnixNano()/int64(time.Millisecond)) > undoThreshold {
 			return
+		} else {
+			if settings["stackundo"] == true {
+				startTime = t.(*TextEvent).time.UnixNano() / int64(time.Millisecond)
+			}
 		}
 
 		eh.UndoOneEvent()

cmd/micro/settings.go

@@ -79,6 +79,7 @@ func DefaultSettings() map[string]interface{} {
 		"ruler":         true,
 		"scrollspeed":   float64(2),
 		"scrollmargin":  float64(3),
+		"stackundo":     false,
 		"statusline":    true,
 		"syntax":        true,
 		"tabsize":       float64(4),

runtime/help/help.md

@@ -211,6 +211,10 @@ Here are the options that you can set:
 
 	default value: `on`
 
+* `stackundo`: reset undothreshold timer to zero if an action is taken before the timer runs out
+
+	default value: `off`
+
 * `scrollmargin`: amount of lines you would like to see above and below the cursor
 
 	default value: `3`