[r-t] Lead head codes

[Philip Earis]

Pip:
> From this it's much easier to see that L, R and B are related by the same
> lead head order, despite having different lead end changes. This
> information is completely obscured using letters of the alphabet as we do
> currently.

I agree that the current system is a mess, but I think you're barking up
the wrong tree when talking about methods like London and Bristol being
related by the same leadend order.

For "regular" methods with palindromic symmetry (ie nearly all rung
methods) then the key information is which bell is the pivot (and hence
which place bells are opposite, which also tells you where bells will be
at the leadend, and which bells cross at the halflead).

Leadend order is an unhelpful distraction.

So for example Cambridge and Glasgow (both 3-pivots) are structurally more
similar than Cambridge and Essex (a 6-pivot), despite Cambridge and Essex
having the same "leadend order".