Release v20.12

[jnbrunet]

Remaining tasks for v20.12:

• Fix all tests in Windows MSVC
• Create a Windows MSVC github workflow
• Clean-up all example scenes file and make sure they work on all supported OS
• Fix the readthedocs automatic builds
• Improve the documentation
• Use SOFA CMake macros for package, modules and targets (see [SofaMacros] Handle COMPONENTS (needed by SofaPython3) sofa#1671)
• Create a release workflow and deploy python binaries alongside the plugin
• Test the release binaries on clean VMs with the installed beta release of SOFA
• Create v20.12 tag