Adds uninstantiable with examples.
Adds uninstantiable with examples.

This closes #1863. It advances #1957, but still some information on
how to use traits in varibles and attributes is going to be needed.

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