The exported Server becomes handlerServer, and part of Presentation
now. Presentation is also now an http.Handler with its own
internal mux (a detail, which might go away).
main.go becomes ever simpler.
R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/11505043
cmd/godoc/godoc.go is now merged into main.go, which is now
only 530 lines.
App Engine mode is still broken, but should be easy to fix up.
(just needs a global *godoc.Presentation created in init)
R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/11498044
