Execution hook for Single

[phajduk]

RxJavaObservableExecutionHook is not compatible with Single type. For example: RxJavaObservableExecutionHook#onCreate method tooks Observable#OnSubscribe type as a parameter. However, Single is using it's own OnSubscribe type. Shall we implement new class to handle Single's hooks let's say RxJavaSingleExecutionHook ?

[akarnokd]

Would you like to post a PR for this?

[phajduk]

If you agree with my proposition then I will create PR for that feature for sure.

[akarnokd]

I don't see anything wrong upfront so go ahead with the PR.