Add in post callback function to simulation

[msatti-metrol]

This PR adds in simulation<>::post() intended as a convenience method for creating an event with callback added, plus scheduling it to run immediately.

Tests included and passing.

[fschuetz04]

I'm unsure whether this helps readability. As far as I understand it, both snippets should behave the same:

sim.post([&ran]() { ran = true; }, 2.0);

auto ev = sim.timeout(2.0);
ev.add_callback([&ran]() { ran = true; });

Personally, I think the second version is readable, while you need to know the post function to understand the first version.

What is the use case for having this special post function?

[msatti-metrol]

both snippets should behave the same

Correct, no difference.

What is the use case for having this special post function?

There was no specific use case for this, more so we are using the same pattern repeatedly in multiple codebases of ours that it made sense to introduce a convenience one-liner function for it:

    void Callbacks_t::StartBitTimerInternal()
    {
        m_bitTimer = m_simulationContext.post(
            [this]()
            {
                    ...
                    StartBitTimerInternal();
            },
            m_bitTimerPeriod.count());
    }

The post name comes from Boost::ASIO, but the functionality is similar to other event loop based frameworks. For example: python. Maybe a change to the name like python would work? call_soon() and call_later()?