examples: fix 14_pause_tween which was trying to use the removed

relative values feature (`start('+500')`) and make it use `.delay(500)`
instead, and avoid using negative values for delaye (`.delay(-500)`) in
the 13_relative_start_time example because it may not be intuitive and
plus that feature broke with the previous merge that fixed more
important timing issues (especially with unfocused browser tabs)

BREAKING: If you are using negative values for delay, f.e.
`tween.delay(-500)`, instead manage the time values passed to your
tweens manually. For example:

```js
tweenOffset = 500
const tween = new Tween(...)
tween.start(currentTime)
tween.update(currentTime + tweenOffset) // advance it immediate immediately, as if it already started earlier

// in the update loop
tween.update(newCurrentTime + tweenOffset)
```

examples/13_relative_start_time.html

@@ -62,8 +62,8 @@ <h2>13 _ relative start time</h2>
 
 				tween2 = new TWEEN.Tween(position2).to({x: 500, y: 300, rotation: -90}, 2000).onUpdate(update2)
 
-				tween1.delay(4000).start()
-				tween2.delay(-500).start()
+				tween1.delay(2000).start()
+				tween2.delay(100).start()
 			}
 
 			function animate(time) {

examples/14_pause_tween.html

@@ -63,7 +63,8 @@ <h2>14 _ pause tween</h2>
 					.onUpdate(update1)
 					.yoyo(true)
 					.repeat(Infinity)
-					.start('+500')
+					.delay(500)
+					.start()
 			}
 
 			function animate(time) {

examples/15_complex_properties.html

@@ -9,7 +9,7 @@
 		<div id="info">
 			<h1><a href="http://github.com/tweenjs/tween.js">tween.js</a></h1>
 			<h2>15 _ complex properties</h2>
-			<p>Simple example for illustrating the creation and chaining of tweens.</p>
+			<p>Simple example for illustrating animation of nested properties.</p>
 		</div>
 		<div
 			id="target"
@@ -38,7 +38,7 @@ <h2>15 _ complex properties</h2>
 				position = {x: 100, y: 100, styles: {opacity: 1.0}}
 				target = document.getElementById('target')
 				tween = new TWEEN.Tween(position)
-					.to({x: 700, y: 200, styles: {opacity: 0.5}}, 1000)
+					.to({x: 700, y: 200, styles: {opacity: 0}}, 1000)
 					.delay(1000)
 					.onUpdate(update)