Work a bit on the Iterator type documentation
Work a bit on the Iterator type documentation

- show some more methods where they are used
- emphasize the fact that a consuming class *can* implement most methods
- some minor signature / output nits

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