Release v0.13.0-rc1

Major changes and bug fixes

1. Upgraded nGraph to v0.19.0

Dependency information

TensorFlow r1.14 Nightly
nGraph v0.19.0

⚠️ Since TensorFlow 1.14 hasn't been published, currently you need to use either the nightly build (tf-nightly==1.14.1.dev20190515) or build TensorFlow 1.14 from source.