Add ad-hoc attrs before adding all class ATTRS.

To account for class ATTRS which may reference the ad-hoc attrs. Although
this seems to indicate a design smell, I don't think it hurts, since
ad-hoc attrs, by definition, won't have configuration methods (setter, getter etc),
so there shouldn't be any order of operation issues adding them before ATTRS.

Also updated APIDocs and HISTORY.md to cover the 'Add all ATTRS at once'
changes a little better.
Added tests for ad-hoc access, order of operations
Build for ad-hoc attrs order of operation change