[release-branch.go1.3] doc: document go1.3.3

««« CL 149280044 / ce32e953ef6f
doc: document go1.3.3

LGTM=r
R=r
CC=golang-codereviews
https://codereview.appspot.com/149280044
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TBR=r
R=golang-codereviews
CC=golang-codereviews
https://codereview.appspot.com/151170043