Add toggleClass() to the animation abstraction

[estaylorco]

I'm submitting a feature request

• Library Version:
  1.0.1

Please tell us about your environment:

• Operating System:
  OSX 10.x

• Node Version:
  7.3.0

• NPM Version:
  3.10.10

• JSPM OR Webpack AND Version
  JSPM 0.16.53

• Browser:
  all

• Language:
  ESNext

Current behavior:
Presently, the animation abstraction offers up addClass() and removeClass(). This leads to code like this:

if (reveal) {
   this.animator.addClass(...);
else {
   this.animator.removeClass(...);
}

Not the end of the world, but a little verbose.

Expected/desired behavior:
I would suggest a toggleClass() method on the abstraction. It is certainly in keeping with many of the animation libraries out there, including jQuery's, and it would allow the above to be reduced to:

this.animator.toggleClass(...);

• What is the motivation / use case for changing the behavior?
  Terseness, clarity, and harmony with many animation libraries' conventional approach.