Feature async render

[PhotoAtomic]

This is my proposed solution to this issue
it was independently developed from the other PR which I've noticed exist only after the facts :( sorry

This solution leverages on the already existing NextRender task without introducing additional synchronization mechanisms like semaphores.
As said in the above mentioned issue, the solution have a little of code duplication, there are easy way to fix it and i'm happy to apply the preferred one, let's just discuss it. options are:

• move common code in a separate method:
  Pros: easy code, Cons: the method should return more than one value => introduced a new return type with multiple properties or uses anonymous records.
• make the divergent portion of code to be called as delegate passing multiple argument to it
  Pros: avoid generation of new types, Cons: less simple code, force to return Task and in case ignore it when not needed
• other...? let's discuss!

I probably prefer the first :)

[PhotoAtomic]

I propose to evaluate #30 instead of this one, because this solution was too rushed and doesn't supports certain scenarios at its current state.