Generic Exception types for ThrowableFuncX

[simplysoft]

ThrowableFunc could be made generic in the Exception it throws, this would eliminate the need for broad catch(Exception e) when you are e.g only dealing with IOExceptions (ThrowableFunc & calling method throws IOException)

public interface ThrowingFunc0<R, E extends Exception> extends Function {
        R call() throws E;
}

If you think this is a good idea, we are happy to prepare a pull request

[akarnokd]

We catch Throwables anyway so it doesn't really matter if it throws Exception or a subclass of exception. See Java's Callable<T> wasn't declared as generic throws.

[simplysoft]

We are also using ThrowingFunc on non rxjava-async related code, so the interface throwing Exception make it is a bit verbose, same problem with Callable<T>. But I can understand if that change is outside the scope of this project