NCBC-627: Create nuspec file for 2.0 SDK

Change-Id: Ib54f3d882b12c6b826053b84cc1ef4988c614263
Reviewed-on: http://review.couchbase.org/41259
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>