Use CMake as our primary build system

Modified Makefile to provide backward compatibility /
convenience methods to build the system. In order to
make it "portable" I've added a GNUmakefile that
gnu make will pick up and set the default values
before using Makefile.

Change-Id: I3247dbfb653810636f580863c77951e008b536c9
Reviewed-on: http://review.couchbase.org/35044
Reviewed-by: Chris Hillery <ceej@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>