Add Documentation (Sphinx) for `on_failure` and `on_success` for both `Try` and `Future` classes

[vickumar1981]

Now that we have on_success and on_failure working for Try and Future, we should add them to the Read the Docs.

https://github.com/vickumar1981/pyeffects/blob/master/docs/future.rst

https://github.com/vickumar1981/pyeffects/blob/master/docs/try.rst