feat(library/data): define 'nat.addl' addition using recursion on the first argument, prove it to be equivalent to 'add', and use it to define vector.append
feat(library/data/nat/order): add calc_trans commands for lt and le
feat(library/data/fin): add fin type
test(tests/lean/run): define div using wf package
refactor(library/logic): add basic definitions for relations at logic/relation.lean

We need them for wf and definitional package
refactor(library/data/nat/sub): cleanup 'max' theorems
test(tests/lean/run/tree_height): experiment with wf relation based on the height

This is easier to generate than the subterm relation
test(tests/lean/run/div_wf): cleanup
test(tests/lean/run/gcd): gcd compiled by hand into wf recursion