fix: apply nullable checks for async inputs

[kylecannon]

async pipe typically emits a null before the value which causes everything to blow up. To correct this, I did the following:

• provided a repro pipe that can be added to "fake" an async call.
• added support for handling async linkTo and linkActive.
• improved typings

There may be other instances I am missing, but this is a start.

[kylecannon]

Thanks for the feedback @brandonroberts. Feedback is addressed.

[brandonroberts]

@kylecannon will you rebase on master? Had to move some things around with the name change

[kylecannon]

@brandonroberts done. Still trying to see what needs to be done though to get this merged. I commented above with a couple of suggestions.