Disptools

* No functional changes.
* Bumped supported Python versions.
* Updated GitHub Actions workflow.
* Removed AppVeyor CI build. Windows wheels are currently unavailable.

New:
* add support for MSVC, now the C extension can be built with Visual Studio
* switch build configuration to CMake
* add alternative GPGPU (CUDA) implementation of the C algorithms
* add continuos integration (AppVeyor)
* move documentation to a separate [gh-pages](https://github.com/m-pilia/disptools/tree/gh-pages) branch

New features:
* add function to decompose displacement fields (https://github.com/m-pilia/disptools/commit/f597ad222919a29a13917bcdd33eac45ff22fa68)
* add function to compute mutual information (https://github.com/m-pilia/disptools/commit/908c0f536c17d5a89349be6794a07ff739cf3a7d, https://github.com/m-pilia/disptools/commit/4db9a4b4939f92ee37d7d4b91bf672d5ed7d5ea7)
* add parameters to control termination of the algorithms for displacement generation (https://github.com/m-pilia/disptools/commit/815d5dbd99ca47fa8baf63110e915766870b81c3)
* add parameter to upper-limit the step length in the algorithms for displacement generation (https://github.com/m-pilia/disptools/commit/f96320bfe4b21e4b799ddda21401d685d979844c)
* add custom color maps to `disptools.drawing.extract_slice` (https://github.com/m-pilia/disptools/commit/6cece45da7f19b553b481ef83e85fa73ae4226c7, https://github.com/m-pilia/disptools/commit/f823cf826c8c505f54a00ec3862aaf95954d91ca)
* add function to convert a binary mask to a Simulatrophy mask (https://github.com/m-pilia/disptools/commit/68ee99ac372381a1e52bcbfa87204f21fe859d46)
* allow handling of non-consistent coordinate systems in the generation of displacements (https://github.com/m-pilia/disptools/commit/b7c027fd9c3d126e3aa7efa97648ef2bf25930db)
* add function to compute image entropy (https://github.com/m-pilia/disptools/commit/5fc197969363faceb6515267e89afe1bb9ea2bb0)
* implement a wrapper to call Simulatrophy (https://github.com/m-pilia/disptools/commit/3123b7cecd97ca05f06f3ee116926762fd77f179)
* higher quality image resampling (https://github.com/m-pilia/disptools/commit/a4380b2770b7b2b1fdbfbeda216f76c6e828bba5)
* add functions to compute Jaccard and F measure (https://github.com/m-pilia/disptools/commit/5a46138ce6f82b9294710e7da3b58dd60727e53e)

API changes:
* rename `disptools.drawing.resize_image` to `disptools.drawing.scale_image` (https://github.com/m-pilia/disptools/commit/b26be21bc4de3edb3e7e430f8712cf5b1fabb8d3)
* change default Jacobian lower thresholds (https://github.com/m-pilia/disptools/commit/c9ce07dae55459bfdf303f01fa2324e17de63763)
* new default parameter values for `disptools.measure.reject_outliers` (https://github.com/m-pilia/disptools/commit/5ec2242f83795fe8914993eee178ade947df8bf1)
* return the standard deviation together with the mean in `disptools.measure.volume_change` (https://github.com/m-pilia/disptools/commit/5ec2242f83795fe8914993eee178ade947df8bf1)

Bug-fixes:
* fix metadata copying in several functions (https://github.com/m-pilia/disptools/commit/c17cfefb5e83820ffbcf0f3b7250c95198a1d097)
* various fixes to `extract_slice` (https://github.com/m-pilia/disptools/commit/900c79dcb0b92668dd2be7141796d69f58a8141e, https://github.com/m-pilia/disptools/commit/e6e3aeec0e2cb0ba831209fa22ae38c53ac001f8, https://github.com/m-pilia/disptools/commit/654a30707a2812d4a8061ea7b8eae407c158167a)
* fix bug related to fractional image spacing (https://github.com/m-pilia/disptools/commit/97f4fba33c73e38b422985b579a214ec75e9ae9e)

*Added regularisation term to the `gradient` algorithm.
*Refactoring of the interface for the `displacements.displacement` function. New default values for the arguments.
*C verbose output to `stdout`, print `eta` at each iteration.
*Implemented `mesure.centre_of_mass`.

Fix a bug in the selection of the algorithm.

Fix bugs due to incomplete copy of SimpleITK image object information in some functions.
Update Sphinx config to automatically read the version number from `setup.py`.

Add MANIFEST.in, fix debug switch macro.