Support CancellationToken

[a046]

Handle #221 architecturally, support CancellationToken in Fire, Actions and Compile.

Not sure about adding it to InsertAll, thoughts?

[snikolayev]

@a046 thank you.
Regarding session insert/update/retract, I don't think cancellation there is helpful or needed. If you cancel propagation of facts in the middle, it would leave the session in an invalid state.

[a046]

Thanks @snikolayev, I was more thinking about the initial seeding of the session with facts (particularly if something like #224 occurs). But it can handled by the consuming code by batching the calls to InsertAll which avoids the complexity.