feat(library/standard/logic): add identities
refactor(library/standard): collect notation in general_notation
refactor(library/standard/data/int): split basic.lean into basic.lean and order.lean
refactor(lean/examples/constable.lean): move to library/standard/logic/examples/nuprl_examples.lean
refactor(lean/examples/constable.lean): move to library/standard/logic/examples/nuprl_examples.lean