move regexp to lib

next cl will update names and add to build

R=rsc
DELTA=1876  (938 added, 938 deleted, 0 changed)
OCL=17149
CL=17166

diff --git a/usr/r/regexp/Makefile b/src/lib/regexp/Makefile
similarity index 100%
rename from usr/r/regexp/Makefile
rename to src/lib/regexp/Makefile

diff --git a/usr/r/regexp/main.go b/src/lib/regexp/main.go
similarity index 100%
rename from usr/r/regexp/main.go
rename to src/lib/regexp/main.go

diff --git a/usr/r/regexp/regexp.go b/src/lib/regexp/regexp.go
similarity index 100%
rename from usr/r/regexp/regexp.go
rename to src/lib/regexp/regexp.go