add "hg gofmt" to run all modified files through gofmt.

add "hg gofmt" to run all modified files through gofmt.

add check before Upload, for now disabled by default,
that files do not change when run through gofmt.
enable by adding

	[codereview]
	force_gofmt = True

to .hgrc or .hg/hgrc.

add doc strings for a few more commands.
rename codereview-login to code-login
to make module doc visible.

R=r
CC=gri
http://go/go-review/1018056