Regular expressions may now be used in conjuction with full text
search. Godoc will show the first 10000 occurences in the source
code and highlight the respective text segments.

- added new flag -testDir to specify a small directory for testing
  (fast index creation; default = "")

- use new FormatText function to format text and Go source
  code in HTML, supporting multiple kinds of text selections
  simulatenously); this replaces the uses of go/printer
  Stylers

- for now removed currently unused mechanism for identifier-
  specific JS popups (will come back in some form once we
  have type or other useful information)

- various typo fixes and minor cleanups throughout

Missing:
- indexing of non-.go files

R=r, r2
CC=golang-dev, rsc
https://golang.org/cl/3699041