Merge tag 'v1.4.4'

1.4.4

 * Add contribution guidelines (Ryan Graham)
Map required/id properties to NOT NULL

See https://github.com/strongloop/strong-arc/issues/600
Merge pull request #26 from strongloop/feature/fix-arc-600

Map required/id properties to NOT NULL
v1.4.5
Merge branch 'release/1.4.5' into production