godoc: enable fulltext index by default

- added flag -maxresults (default: 10000) to limit the max.
  number of full text results shown
- removed flag -fulltext; use -maxresults=0 to disable fulltext
  index
- better indication on result page if not all results are shown
  (... after line list)

R=rsc, gri1
CC=golang-dev
https://golang.org/cl/4049042
4 files changed