Prefer pointers for method receivers

Google's "Go Code Review Comments" document takes a different approach to pointer/value receivers than is currently noted in this comment, where they seem to prefer pointer receivers:
https://code.google.com/p/go-wiki/wiki/CodeReviewComments#Receiver_Type

This change is a small summary of the points outlined in the linked document.
Merge pull request #1 from ctl80/patch-1

Prefer pointers for method receivers