This also includes some of the samples project.json feed discussed like remove version attribute, changing case of Kestrel to 'kestrel'
Fixing the nuget.config feed to point to the new feed for master.
Fixing readme with a pinned build of KRE.
1. Updated samples to use Kestrel for cross plat
2. Updated "configurations" in project.json to "frameworks"
3. Updated readme to include instructions on Kestrel