feat(frontends/lean): send tactic hint table to elaborator

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(tests/lean/run): add test_single script that sets the LEAN_PATH

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(tests): cleanup test scripts

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(tests): add missing tests

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(.): add make.deps to .gitignore

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean): add basic tactics

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean): use tactics for solving unassigned metavariables

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>