Minkowskiengine

- Fix `TensorField.sparse()` for no duplicate coordinates
- Skip unnecessary spmm if `SparseTensor.initialize_coordinates()` has no duplicate coordinates
- Model summary utility function added
- TensorField.splat function for splat features to a sparse tensor
- SparseTensor.interpolate function for extracting interpolated features
- `coordinate_key` property function for `SparseTensor` and `TensorField`
- Fix .dense() for GPU tensors. (PR 319)

- Updated README for pytorch 1.8.1 support
- Use custom `gpu_storage` instead of thrust vector for faster constructors
- pytorch installation instruction updates
- fix transpose kernel map with `kernel_size == stride_size`
- Update reconstruction and vae examples for v0.5 API
- `stack_unet.py` example, API updates
- `MinkowskiToFeature` layer

- spmm average cuda function
- SparseTensor list operators (cat, mean, sum, var)
- MinkowskiStack containers
- Replace all at::cuda::getCurrentCUDASparseHandle with custom getCurrentCUDASparseHandle (issue 308)
- fix coordinate manager kernel map python function
- direct max pool
- SparseTensorQuantizationMode.MAX_POOL
- TensorField global max pool
- origin field
- origin field map
- MinkowskiGlobalMaxPool CPU/GPU updates for a field input
- SparseTensor.dense() raises a value error when a coordinate is negative rather than subtracting the minimum coordinate from a sparse tensor. (issue 316)
- Added `to_sparse()` that removes zeros. (issue 317)
- Previous `to_sparse()` was renamed to `to_sparse_all()`
- `MinkowskiToSparseTensor` takes an optional `remove_zeros` boolean argument.
- Fix global max pool with batch size 1
- Use separate memory chunks for in, out map, and kernel indices for `gpu_kernel_map` for gpu memory misaligned error

- v0.5 documentation updates
- Nonlinear functionals and modules
- Warning when using cuda without ME cuda support
- diagnostics test
- TensorField slice
- Cache the unique map and inverse map pair in the coordinate manager
- generate inverse_mapping on the fly
- CoordinateManager
- `field_to_sparse_insert_and_map`
- `exists_field_to_sparse`
- `get_field_to_sparse_map`
- fix `kernel_map` with empty coordinate maps
- CoordiateFieldMap
- `quantize_coordinates`
- TensorField binary ops fix
- MinkowskiSyncBatchNorm
- Support tfield
- convert sync batchnorm updates
- TensorField to sparse with coordinate map key
- Sparse matrix multiplication
- force contiguous matrix
- Fix AveragePooling cudaErrorMisalignedAddress error for CUDA 10 (246)

Major speedup with GPU coordinate map/manager backend.