When you select a date, show the rules of succession

[neilb]

My understanding (I don't pay much attention to this though, you understand) is that the rules of succession have changed, for example with respect to primogeniture.

When a date is selected, you could have a sidebar that succinctly summarises the rules of succession at that time.

Also have a link to the best source on rules of succession for the British monarchy. No idea if that is the wikipedia page on it, or somewhere else ...