Also fix salt expansion code to fill the properly sized array,
since the following code never uses more than 4 uints.
Also remove unused expandedKey array.
R=golang-dev, agl
CC=golang-dev
https://golang.org/cl/6622050
Manual edits to README.
Moved from main Go repository, deleted Makefiles, ran gofix -r go1rename.
Tested with: go test code.google.com/p/go.crypto/...
R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5564059