src: add license content from ICU

Added license info from:
 http://source.icu-project.org/repos/icu/icu/trunk/license.html


All text pasted. Long lines wrapped. (original is HTML.)

Reviewed-By: Julien Gilli <julien.gilli@joyent.com>
Reviewed-By: Timothy J Fontaine <tjfontaine@gmail.com>