Document IO::Path.parent(UInt)
Document IO::Path.parent(UInt)

Spec:        https://github.com/perl6/roast/commit/bf3f347e11
             https://github.com/perl6/roast/commit/1b39fb200c
Rakudo impl: https://github.com/rakudo/rakudo/commit/7bea3a2dddcfc11
Closes https://github.com/perl6/doc/issues/1616 D#1616

jonathanstowe/doc,jonathanstowe/doc,MasterDuke17/doc,dmaestro/doc,MasterDuke17/doc,MasterDuke17/doc,perl6/doc,perl6/doc,jonathanstowe/doc,stmuk/doc,dmaestro/doc,jonathanstowe/doc,stmuk/doc,MasterDuke17/doc,tbrowder/doc,stmuk/doc,stmuk/doc,perl6/doc,perl6/doc,tbrowder/doc,stmuk/doc,jonathanstowe/doc,tbrowder/doc,perl6/doc,dmaestro/doc,dmaestro/doc,dmaestro/doc,tbrowder/doc