feat(frontends/lean/scanner): allow '#' to be used in class B identifiers

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean/parser): allow 'typeless' definitions, the type is inferred by the system

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(lua): add Lua support to build

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