use tcell via porting over code from awesome-gocui

vendor/github.com/jesseduffield/gocui/loader.go

@@ -0,0 +1,46 @@
+package gocui
+
+import "time"
+
+func (g *Gui) loaderTick() {
+	go func() {
+		for range time.Tick(time.Millisecond * 50) {
+			for _, view := range g.Views() {
+				if view.HasLoader {
+					g.userEvents <- userEvent{func(g *Gui) error { return nil }}
+					break
+				}
+			}
+		}
+	}()
+}
+
+func (v *View) loaderLines() [][]cell {
+	duplicate := make([][]cell, len(v.lines))
+	for i := range v.lines {
+		if i < len(v.lines)-1 {
+			duplicate[i] = make([]cell, len(v.lines[i]))
+			copy(duplicate[i], v.lines[i])
+		} else {
+			duplicate[i] = make([]cell, len(v.lines[i])+2)
+			copy(duplicate[i], v.lines[i])
+			duplicate[i][len(duplicate[i])-2] = cell{chr: ' '}
+			duplicate[i][len(duplicate[i])-1] = Loader()
+		}
+	}
+
+	return duplicate
+}
+
+// Loader can show a loading animation
+func Loader() cell {
+	characters := "|/-\\"
+	now := time.Now()
+	nanos := now.UnixNano()
+	index := nanos / 50000000 % int64(len(characters))
+	str := characters[index : index+1]
+	chr := []rune(str)[0]
+	return cell{
+		chr: chr,
+	}
+}