More unit testing of Migrations.
Check to make sure we don't run our migrations-checking code twice.
Finish spec for Migrations.
Documentation for LowCardTables::ActiveRecord::Migrations.
Fix small bug I introduced that the system spec caught; also, make sure the unit spec catches it now, too.
Documentation and spec for LowCardTables::ActiveRecord::Relation.
Documentation and spec for LowCardTables::ActiveRecord::Scoping.