Document inferred name in Polymer() call

This replaces #530, which got a little confused.

Rewriting to reflect the new support for inferred names nearly everywhere required more rewriting than I thought.

PTAL, @sjmiles @sorvell 
Not sure how to describe that. Physically, it's the difference between tying two object together with string (chaining) and painting on one object (modifying). I wouldn't have even occurred to me to mention explicitly that we modify the prototype object .. we modify everything, this is what the sugaring is for. Sorry if I totally failed to answer your question.