[io grant] Document IO::Special.what
[io grant] Document IO::Special.what

Split off part of .new prose and list .what as a separate section,
since it is a public attribute.

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