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
fix(library/tools/tactic): 'cases' argument precedence
feat(library/tactic): add 'assert' tactic, closes #349
refactor(library/logic/heq): minor change
test(tests/lean/run/vector): use nat.add
refactor(data/nat/decl): use new naming convention at data/nat/decl.lean
chore(library/data/nat/decl): remove leftover
feat(frontends/lean): add 'prelude' command, and init directory
refactor(library): add 'init' folder
fix(tests/lean): adjust tests to modifications to standard library
chore(library/logic/logic.md): adjust documentation
fix(library/tactic/inversion_tactic): uninitialized variable
refactor(library/init): move num->nat coercion to init
test(tests/lean/slow): add "manual" 'path induction' tactic