Width modifiers

I have completed 

ACTION A-643-01: MikeK to update proposal on Bug 29555. 

(relating to width modifiers in format-date() and friends)

attempting to take comments into account.

In particular, I have bitten the bullet on the rules for fractional seconds, with a rather weird algorithm that appears to give the right result. Please check it and comment.

https://www.w3.org/Bugs/Public/show_bug.cgi?id=29555#c15

Michael Kay
Saxonica