Add option to run enter and leave animations in parallel

Author: blikblum

lib/components/animated-outlet.js

@@ -11,6 +11,10 @@ export class AnimationHook {
     return outlet.hasAttribute(name) || this.options[name]
   }
 
+  runParallel (outlet) {
+    return this.hasOption(outlet, 'parallel')
+  }
+
   beforeAdd (outlet, el) {
 
   }
@@ -212,10 +216,11 @@ export class AnimatedOutlet extends HTMLElement {
       return
     }
     const hook = getAnimationHook(this.getAttribute('animation'))
+    const runParallel = hook.runParallel(this)
 
     hook.beforeAdd(this, el)
     super.appendChild(el)
-    if (this.removing) {
+    if (!runParallel && this.removing) {
       // when removing a previous el, append animation is run after remove one
       this.appending = el
     } else {