Updates pause functionality (#32)

* feat: [add-pause-functionality] Adds Spacebar Pausing

Adds pausing to the countdown timer by using the spacebar key.
Also added an input delay in order to avoid pausing happening
immediately when the space bar button is pressed.

* feat: [update-pause-functionality] Updates Pause

Updates the pause functionality with the following:
1. Adds pause font in the lower 3/4 of the screen
2. Changes the button press to require a spacebar instead of 'p' and 'c'
3. Adds an input buffer timeout so you don't accidentally pause and
   unpause with one button press.
4. When unpausing, adds another call of the draw function so that the
   'Paused' text is immediately removed instead of waiting for the next
   tick.

font.go

@@ -90,3 +90,8 @@ var defaultFont = Font{
 		" ╚════╝ ",
 	},
 }
+
+var pausedText = Symbol{
+	"█▀▄ ▄▀▄ █ █ ▄▀▀ ██▀ █▀▄",
+	"█▀  █▀█ ▀▄█ ▄██ █▄▄ █▄▀",
+}

main.go

@@ -22,7 +22,8 @@ const (
 
  Flags
 `
-	tick = time.Second
+	tick         = time.Second
+	inputDelayMS = 500 * time.Millisecond
 )
 
 var (
@@ -31,6 +32,8 @@ var (
 	queues         chan termbox.Event
 	startDone      bool
 	startX, startY int
+	inputStartTime time.Time
+	isPaused       bool
 )
 
 func main() {
@@ -80,6 +83,7 @@ func stop() {
 
 func countdown(timeLeft time.Duration, countUp bool, sayTheTime bool) {
 	var exitCode int
+	isPaused = false
 
 	start(timeLeft)
 
@@ -96,16 +100,24 @@ loop:
 	for {
 		select {
 		case ev := <-queues:
-			if ev.Type == termbox.EventKey && (ev.Key == termbox.KeyEsc || ev.Key == termbox.KeyCtrlC) {
+			if ev.Key == termbox.KeyEsc || ev.Key == termbox.KeyCtrlC {
 				exitCode = 1
 				break loop
 			}
-			if ev.Ch == 'p' || ev.Ch == 'P' {
-				stop()
-			}
-			if ev.Ch == 'c' || ev.Ch == 'C' {
-				start(timeLeft)
+
+			if pressTime := time.Now(); ev.Key == termbox.KeySpace && pressTime.Sub(inputStartTime) > inputDelayMS {
+				if isPaused {
+					start(timeLeft)
+					draw(timeLeft)
+				} else {
+					stop()
+					drawPause()
+				}
+
+				isPaused = !isPaused
+				inputStartTime = time.Now()
 			}
+
 		case <-ticker.C:
 			if countUp {
 				timeLeft += tick
@@ -148,6 +160,15 @@ func draw(d time.Duration) {
 	flush()
 }
 
+func drawPause() {
+	w, h := termbox.Size()
+	startX := w/2 - pausedText.width()/2
+	startY := h * 3 / 4
+
+	echo(pausedText, startX, startY)
+	flush()
+}
+
 func format(d time.Duration) string {
 	d = d.Round(time.Second)
 	h := d / time.Hour