fix(library/standard/nat2): remove spurious commas in calc proof

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/standard/extract_deps): used new --deps command line option for computing the precise dependencies of a .lean file

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(library/standard/nat2): proved x = x div y * y + x mod y
fix(library/standard): fix typo, comment unfinished theorems
fix(library/standard/Makefile,extract_deps): use ENV_VAR LEAN if exists