Improve multi method documentation: named parameters.
Improve multi method documentation: named parameters.

See issue #2026

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