Migrating to 4.0.0

[KasperSK]

Let us use this issue to discuss the detail for writing the migrating to 4.0.0 section.

I can see that there is all ready some work that has been started by Nigel I think we should expand upon that.

Migrating to 4.0.0

[mbreckon]

I've just tried upgrading the NuGet package of one of my apps from 3.2 to 4.0.136-rc. There are two categories of breaking changes - event handler async and lifecycle async (as expected based on the Migrating to 4.0.0 document).

(aside: It is frustrating that the links within the pages on github are broken but without giving it too much thought I guess this is because of the relative links)

I think there are a few things that can be done to clarify the event aggregator documentation. I'll create a PR to capture those. I'll have to look at the lifecycle stuff separately.