Torch-lr-finder

What's Changed
* Explicitly check whether `min_grad_idx` is `None` or not before returning in `lr_finder.plot()` by NaleRaphael in https://github.com/davidtvs/pytorch-lr-finder/pull/66
* Update CI by davidtvs in https://github.com/davidtvs/pytorch-lr-finder/pull/92
* Make both `torch.amp` and `apex.amp` available as backend for mixed precision training by NaleRaphael in https://github.com/davidtvs/pytorch-lr-finder/pull/91
* Update CI to python 3.6 and torch 1.0.0 by davidtvs in https://github.com/davidtvs/pytorch-lr-finder/pull/95
* Prevent unexpected unpacking error when calling `lr_finder.plot()` with `suggest_lr=True` by NaleRaphael in https://github.com/davidtvs/pytorch-lr-finder/pull/98
* Fix ci-build status badge and link status badge to actions by drichardson in https://github.com/davidtvs/pytorch-lr-finder/pull/99
* Bump the action-dependencies group with 4 updates by dependabot in https://github.com/davidtvs/pytorch-lr-finder/pull/100
* Update release action by davidtvs in https://github.com/davidtvs/pytorch-lr-finder/pull/101

New Contributors
* drichardson made their first contribution in https://github.com/davidtvs/pytorch-lr-finder/pull/99
* dependabot made their first contribution in https://github.com/davidtvs/pytorch-lr-finder/pull/100

**Full Changelog**: https://github.com/davidtvs/pytorch-lr-finder/compare/v0.2.1...v0.2.2

Release notes:
- Fix error message in `DataLoaderIter.inputs_labels_from_batch()`
- Fix flat loss when using a validation dataset (59, 60)
- Fix issue 57 by determining the batch size from the size of the labels instead of the size of the inputs (58)
- Add optional argument to `LRFinder.plot()` for plotting a suggested learning rate (44). The optional argument is `suggest_lr`

Release notes:
- Command to install apex changed from `pip install torch-lr-finder -v --global-option="amp"` to `pip install torch-lr-finder -v --global-option="apex"`
- Handle apex install for pytorch < 1.0.0
- Remove message checking if the `apex.amp` module is available (46)
- Fix learning rate history and learning rate computation in schedulers (43, 42)
- Refactor of Dataloader iterator wrapper (37). An example of how this can be used can be found in [examples/lrfinder_cifar10_dataloader_iter](https://github.com/davidtvs/pytorch-lr-finder/blob/master/examples/lrfinder_cifar10_dataloader_iter.ipynb)
- Transfer data to cuda with non_blocking=True (31)
- Enable batch data contained in a dictionary to be moved to the correct device (29)
- Enable generic objects to be moved to the correct device if they have a `.to()` method (29)
- Dropped Python 2.x support: the last version with Python 2 support is v0.1.5 which can also be found in the [torch_lr_finder-v0.1](https://github.com/davidtvs/pytorch-lr-finder/tree/torch_lr_finder-v0.1) branch

Fixed extended iterable unpacking for Python 2.7 as proposed by NaleRaphael in 27.