feat(frontends/lean/parser): add support for integer arguments in macros

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(frontends/lean/parser): macro precedence

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(extra): replace parse_lean_tpl with improved parse_template, that is based on macros

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