cmd/godoc: cleanups

- removed gratuitous empty lines that creeped into command line output
- changed comment color to a dark green so that links don't visually melt into them
- removed some TODOs
- updated doc.go

R=golang-dev, bradfitz
CC=golang-dev
https://codereview.appspot.com/8108044
net/http: remove two more server allocations per-request

benchmark                                   old ns/op    new ns/op    delta
BenchmarkServerFakeConnWithKeepAliveLite        11031        10689   -3.10%

benchmark                                  old allocs   new allocs    delta
BenchmarkServerFakeConnWithKeepAliveLite           23           21   -8.70%

benchmark                                   old bytes    new bytes    delta
BenchmarkServerFakeConnWithKeepAliveLite         1668         1626   -2.52%

R=golang-dev, gri
CC=golang-dev
https://codereview.appspot.com/8110044