v2.1.0

Improve the types of exported throttle function to improve inference instead of requiring explicit generics.
Add throttleAsync and trailingDebounceAsync throttle functions for additional throttling options.
All throttle functions now return IGNORE_RESULT unique symbol when they early return because of cancelled execution. Previously, they returned undefined which would likely overlap with the return of the function being invoked.
Export reduceUndefined and improve its type.
Change target of tsconfig to ESNext
Validators can now no longer run concurrently with themselves.
Remove async-validator optimization as a result of disabling concurrent executions
Added validateIf built-in validator
Added test for validateIf
Added test for making sure intermediate validations are skipped (performance test).
Update README significantly.