Add support of dio cancel tokens

[vasilich6107]

trafficstars

Description In case of simple search input while user is typing I'm spawning new request and I want co cancel old one if it is in progress

[ahmednfwela]

since exposing dio's cancel token class would tightly couple this package with dio, what do you think about this solution?

https://stackoverflow.com/a/54905898/4009642