LibreSSL 2.0 (new formula)

Add a formula for the [first portable release](http://marc.info/?l=openbsd-tech&m=140510291304119&w=2) of [LibreSSL](http://www.libressl.org/), OpenBSD's fork of OpenSSL.
Should I add ``` :provided_by_osx ``` here, or not since this is an independent fork?