refactor(library/data/int/basic): make the integers an instance of ring
refactor(*): add uniform names for "meta-objects"
fix(library/data/int): define sub from algebra.sub
fix(data/int/basic): move decidable theorems
fix(tests/lean/run): replace "open [notation]" with "open [notations]"
fix(tests/lean/run): replace "open [notation]" with "open [notations]"