Generate fast XS accessors without runtime compilation

The module implements fast XS accessors both for getting at and setting an
object attribute. Additionally, the module supports mutators and simple
predicates (has_foo() like tests for definedness of an attributes). The
module works only with objects that are implemented as arrays. Using it on
hash-based objects is bound to make your life miserable. Refer to
Class::XSAccessor for an implementation that works with hash-based objects.