Add Royal Wedding bank holiday to UK calendar.

Thanks to Whit Armstrong for the heads-up.
Remove unused assignment.

The value is overwritten a few lines later.
Avoid shadowing data member with constructor argument.

This could cause the data member to be given a null value.
Remove duplicated assignments.
Remove unused test parameter.
Removed extra calculations.

Apparently, they were added to nudge the compiler into not
optimizing method calls away. They were replaced by a proper
update method.
Allow auto-linking for VC++12.

We still don't have projects for VC++12; this change allows one
to use the VC++11 solution and auto-link the generated library.
Update changelog.