various implementation of collation.  The tool provides commands for soring,
regressing one implementation against another, and benchmarking.
Currently it includes collation implementations for the Go collator, ICU,
and one using Darwin's CoreFoundation framework.
To avoid building this tool in the default build, the colcmp tag has been
added to all files. This allows other tools/colcmp in this directory (e.g. it may make
sense to move maketables here) to be put in this directory as well.

R=r, rsc, mpvl
CC=golang-dev
https://golang.org/cl/6496118