Mediapipe

* Support Bazel 2 and 3. MediaPipe will no longer support Bazel 0.x and 1.x.
* MediaPipe's TensorFlow dependency is now pointing to https://github.com/tensorflow/tensorflow/commit/805e47cea96c7e8c6fccf494d40a2392dc99fdd8, which is submitted on April 1, 2020.
* MediaPipe's Protobuf dependency is now pointing to [protobuf-3.11.4](https://github.com/protocolbuffers/protobuf/releases/tag/v3.11.4).
* Solve Xlib's Status & absl::Status compilation issue on linux.
* Fix setup_opencv.sh.
* Fix media sequence documentation by following the suggestions in https://github.com/google/mediapipe/issues/566.

* CPU acceleration with [XNNPack](https://github.com/google/XNNPACK)
* Fix iOS memory leak issue: https://github.com/google/mediapipe/issues/387
* Support detection proto in MediaPipe AAR
* Add hair segmentation desktop live demo
* [Google Open Source code search for MediaPipe Github repository](https://cs.opensource.google/mediapipe/mediapipe)

* [MediaPipe Objectron](https://solutions.mediapipe.dev/objectron) (3D object detection and tracking using only RGB images)
* [Objectron calculators](https://github.com/google/mediapipe/tree/master/mediapipe/graphs/object_detection_3d/calculators)
* See also [Google AI Blog post](https://ai.googleblog.com/2020/03/real-time-3d-object-detection-on-mobile.html)
* Bug fixes
* Update Coral dependences to match v0.6.9 release

* MediaPipe's Abseil dependency is now pointing to [abseil's LTS_2020_02_25 release](https://github.com/abseil/abseil-cpp/releases/tag/20200225).
* MediaPipe is now switched to [absl::Status](https://github.com/abseil/abseil-cpp/tree/master/absl/status).
* MediaPipe's TensorFlow version is now pointing to [commit 77e9ffb9b2bfb1a4f7056e62d84039626923e328](https://github.com/tensorflow/tensorflow/commit/77e9ffb9b2bfb1a4f7056e62d84039626923e328), which is submitted on Feb 12, 2020.
* The range of Bazel version that MediaPipe supports is now narrowed. We support Bazel from v1.0.0 to v1.2.1.

* improved android camera support (camera properties including).
* subgraph node and stream naming improvement
* bug fix for data race in SimulationClockExecutor
* concurrency macros update for ABSL (GUARDED_BY --> ABSL_GUARDED_BY)
* image_cropping_calculator improvement.
* new utility calculator, ConstantSidePacketCalculato
* Web demos
* [Edge Detection](https://viz.mediapipe.dev/runner/demos/edge_detection/edge_detection.html)
* [Face Detection](https://viz.mediapipe.dev/runner/demos/face_detection/face_detection.html)
* [Hands Tracking](https://viz.mediapipe.dev/runner/demos/hand_tracking/hand_tracking.html)
* [Hair Segmentation](https://viz.mediapipe.dev/runner/demos/hair_segmentation/hair_segmentation.html)
* Documentation
* Corel example improvement
* [YouTube channel](https://www.youtube.com/channel/UCObqmpuSMx-usADtL_qdMAw)
* [MediaPipe on the Web - Google Dev Blog Post](https://developers.googleblog.com/2020/01/mediapipe-on-web.html)

* [MediaPipe AutoFlip desktop example](https://github.com/google/mediapipe/tree/master/mediapipe/examples/desktop/autoflip)
* Bazel maximum version check (version 1.2.1)
* [Added way to extract detection protos from object detection android mobile GPU example](https://github.com/google/mediapipe/commit/ae6be10afe59a6a99d8a68007784706ac98720dd#diff-e2d9229283509a972282c1d03f41ec3d)
* Bug fixes
* previous_loopback_calculator
* split_vector_calculator
* scale_image_calculator
* Documentation
* [MediaPipe AutoFlip documentation](https://github.com/google/mediapipe/blob/master/mediapipe/docs/autoflip.md)
* Fixes for [framework concept](https://github.com/google/mediapipe/commit/ae6be10afe59a6a99d8a68007784706ac98720dd#diff-31805dad11a7299bfc5fa68e64a3611a), [coral face](https://github.com/google/mediapipe/commit/ae6be10afe59a6a99d8a68007784706ac98720dd#diff-44a9f2c7d5adb5e036037bc747a4365a) and [object detection](https://github.com/google/mediapipe/commit/ae6be10afe59a6a99d8a68007784706ac98720dd#diff-dab963cc487732c4c0640be442119e2c) docs