[RFC] Make a migration guide from 1.0.2 -> 2.0.0

[Alizter]

As I mentioned on discourse. I think the top priority for this repo would be to have a migration guide for all the libraries depending on 1.0.2.

A good way to write this would be to open a draft PR and then go about converting various projects to 2.0.0, documenting the API changes that were needed in order to do this.

I should note that I have 0 experience with using camomile, so my viewpoint will necessarily be fresh.

I am open to any comments of suggestions for making this process smoother.

Of course, if we know some simple migration tips we should also write those down.