Update book to Rx 4

[kibin]

I couldn’t follow through example in introduction with double clicks until I found on SO that throttle is now a delay, which is quite confusing

[xgrommx]

@kibin All docs about operators will be update according with official docs.

[vvscode]

TypeError: scheduler.startWithTiming is not a function on running code from http://xgrommx.github.io/rx-book/content/getting_started_with_rxjs/testing_and_debugging.html ( according documentation method is still in TestScheduler interface -- maybe you can say how to fix? )