Lobe

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Bug Fixes and Other Improvements
* Add support for Python 3.10, drop support for Python 3.6.
* Bump requirements to latest versions.
* Update Raspberry Pi and setup install to latest tensorflow-lite guidance.

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Bug Fixes and Other Improvements
Fix super invocations for onnx and tflite backends -- Calling `predict()` was broken because `self.lock` has not been
assigned.

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Breaking Changes
* Refactored the ML backends into sub-folders:
* `TFModel` class: `backends/backend_tf.py -> backends/tf/backend.py`
* `TFLiteModel` class: `backends/backend_tflite.py -> backends/tflite/backend.py`
* `ONNXModel` class: `backends/backend_onnx.py -> backends/onnx/backend.py`

Bug Fixes and Other Improvements
* Added `Backend` and `ImageBackend` abstract base classes in `backends/backend.py`
* Added ImageBackend classes for each ML backend:
* `TFImageModel` class: `backends/tf/image_backend.py`
* `TFLiteImageModel` class: `backends/tflite/image_backend.py`
* `ONNXImageModel` class: `backends/onnx/image_backend.py`
* Added Grad-CAM++ implementation (`ImageBackend.gradcam_plusplus(image, label) -> np.ndarray`) for visualizing
convolutional neural network heatmaps for explaining why the model predicted a certain label.
_Note:_ Grad-CAM++ only implemented currently in `TFImageModel` for TensorFlow Lobe model exports.
The visualization can be called from the top-level API of `ImageModel` -> `ImageModel.visualize(image)`

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Breaking Changes
* Install Lobe with your desired backend options through pip -- `pip install lobe[all]` for everything,
`pip install lobe[tf]` for tensorflow, `pip install --index-url https://google-coral.github.io/py-repo/ tflite_runtime; pip install lobe` for tensorflow lite, `pip install lobe[onnx]` for onnx.

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Bug Fixes and Other Improvements
* Fix API return signature for Lobe 0.9
* Make backwards-compatible with earlier versions of model exports

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Breaking Changes
* Previous use of Signature should be ImageClassificationSignature. `from lobe.signature import Signature` ->
`from lobe.signature import ImageClassificationSignature`

Bug Fixes and Other Improvements
* Update to TensorFlow 2.4 from 1.15.4
* Add ONNX runtime backend
* Use requests instead of urllib
* Make backends thread-safe
* Added constants file for signature keys to enable backwards-compatibility