chore(.gitignore): add .lean_options

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

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(kernel/inductive): replace recursor name, use '.rec' instead of '_rec'

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