test(tests/lean/run/vector): define 'map' on vector using brec_on and new inversion tactic
feat(frontends/lean/builtin_cmds): display 'print' command output as flycheck information
fix(frontends/lean/calc): add expected type for single-step calc expressions, fixes #357

This is not an issue for calc expressions containing multiple steps,
since the transitivity step will "force" the expected type for the proofs.
fix(frontends/lean/parser): user provided numeral notation should have precedence over the default based on 'num'
feat(frontends/lean): allow expressions to be used to define precedence, closes #335
refactor(library): use "symbolic" precedences in the standard library
feat(library/tactic): add 'fapply' tactic, closes #356