feat: [#242] Implement Parallel Actions

[eonarheim]

===:clipboard: PR Checklist :clipboard:===

• 📌 issue exists in github for these changes
• 🔬 existing tests still pass
• 🙈 code conforms to the style guide
• 📐 new tests written and passing / old tests updated with new scenario(s)
• 📄 changelog entry added (or not needed)

==================

Closes #242

This PR implements 2 new Action types to enable running parallel actions. ActionSequence which allows developers to specify a sequence of actions to run in order, and ParallelActions to run multiple actions at the same time.

Example, moves the actor in a box while rotating it at the same time

var sequence1 = new ex.ActionSequence(actor, ctx => {
  ctx.easeBy(ex.vec(200, 0), 1000, ex.EasingFunctions.EaseInOutCubic);
  ctx.delay(500);
  ctx.easeBy(ex.vec(0, 200), 1000, ex.EasingFunctions.EaseInOutCubic);
  ctx.delay(500);
  ctx.easeBy(ex.vec(-200, 0), 1000, ex.EasingFunctions.EaseInOutCubic);
  ctx.delay(500);
  ctx.easeBy(ex.vec(0, -200), 1000, ex.EasingFunctions.EaseInOutCubic);
  ctx.delay(500);
});

var sequence2 = new ex.ActionSequence(actor, ctx => {
  ctx.rotateBy(Math.PI, Math.PI, ex.RotationType.Clockwise);
  ctx.delay(500);
  ctx.rotateBy(Math.PI, Math.PI, ex.RotationType.CounterClockwise);
  ctx.delay(500);
  ctx.rotateBy(Math.PI, Math.PI, ex.RotationType.Clockwise);
  ctx.delay(500);
  ctx.rotateBy(Math.PI, Math.PI, ex.RotationType.CounterClockwise);
  ctx.delay(500);
});

var parallel = new ex.ParallelActions([sequence1, sequence2]);

actor.actions.repeatForever(ctx => ctx.runAction(parallel));

Changes:

• Fix some bugs in existing action types
• Add the missing EaseBy action type
• Add new ActionSequence action type
• Add new ParallelActions action type