Add Axiom::Relation::Header#size
Refactor code testing the header size to use Relation::Header#size
Refactor Header#initialize to set an ivar and use attr_reader
Refactor Header#coerce to be simpler
Add Axiom::Tuple#size
Remove completed TODO item
Add TODO notes for adding aggregate methods to Axiom::Relation
Fix specs to work with Infinity change to singleton object
Change flay and reek thresholds