[CHANGES]

• Added inherit and apply keywords in an attempt to make
  subclassing and role-application more flexible in future
  
• Experimental new ability to "import" fields from superclasses into
  subclasses, permitting subclasses to interact with base class
  fields directly
  
• Allow setting the OBJECTPAD_FLAG_ATTR_*_VALUE flags when
  registering a custom attribute via the Perl-level MOP API