Add a short introduction to subroutines and precedence dropping.
Add a short introduction to subroutines and precedence dropping.

Should help removing the TODO tag on this section.
The subroutine are now briefly explained in the section, and the example
contains a reference to the hyper method call ">>".

A new head2 section about precedence dropping has been created
with a short example about the difference on using a "standard" method call
and a precedence drop one.

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