Revise the semantics of facade

[mingxwa]

Major changes

• Added type proxy_pointer_constraints, encapsulating maximum_size, maximum_alignment, minimum_copyability, minimum_relocatability and minimum_destructibility into a single type.
• Added 3 prototypes of proxy_pointer_constraints with popular configurations: relocatable_pointer_constraints, copyable_pointer_constraints and trivial_pointer_constraints.
• Added concept basic_facade and concept facade.
• Removed class templates dispatch and facade.
• Added macro PRO_MAKE_DISPATCH_PACK as an extension.
• Added PRO_ prefix to the existing macros to avoid collision.
• Revised the semantics of extension PRO_DEF_FACADE, making it easier to use.

Other changes

• Replaced the SFINAE guarantee of basic_facade_traits with concept facade.
• Removed flattening_traits in the implementation of dispatch_traits.
• Updated unit tests accordingly.