Fix base implementation.
Write tests for lifts & filters.
Write more tests for combinatorial functions.
Rearrange code a little.
Add more tests for post dependent operators.
Commit changes only after subscribers are notified.
Throw TypeError on wrong signal inputs.
Simplify fold implementation.
Simplify past dependent API implementations.
Write tests dropRepeats.
Write tests for keepWhen.
Write tests for dropWhen
Write tests for sampleOn.