[CHANGES]

• Defined new ABI version for class/slot hooks
  
  • Adds funcdata at registration and callback time
    
  • Adds MOP accessor functions for slotmeta default SV
    
• Added :isa() and :does() class attributes; encourage those rather
  than the older keyword style
  
• Added more MOP methods:
  
  • $classmeta->direct_methods, ->get_direct_method
    
  • $classmeta->all_methods, ->get_method
    
  • $slotmeta->has_attribute, ->get_attribute_value
    
• Added Object::Pad::MOP::SlotAttr, allowing pure-perl slot
  attributes that provide simple metadata storage