text/template: new, simpler API
The Set type is gone. Instead, templates are automatically associated by
being parsed together; nested definitions implicitly create associations.
Only associated templates can invoke one another.
This approach dramatically reduces the breadth of the construction API.
For now, html/template is deleted from src/pkg/Makefile, so this can
be checked in. Nothing in the tree depends on it. It will be updated next.
R=dsymonds, adg, rsc, r, gri, mikesamuel, nigeltao
CC=golang-dev
https://golang.org/cl/
5415060