introduce meaningful section names, so that
introduce meaningful section names, so that

	go_spec.html#Return_statements

can be used to link to spec sections.  passes hlint.
renamed final section to simply "Implementation differences"
to shorten the name, but otherwise no non-formatting changes

R=gri
DELTA=230  (10 added, 0 deleted, 220 changed)
OCL=33598
CL=33598

firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang-old,wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang,wesolows/golang,firebitsbr/golang-old