v0.6.3

v0.6.3 Mainly consists of small patches and continuous updates for dependent software and CI systems.
It also extends the tutorials and notebook based documentation.

• cufinufft v1.2 Updates
• Update Example Notebooks and add a more comprehensive demonstration
• Replace Travis CI with GitHub Actions
• Migrate GitHub Pages Documentation to GitHub Actions
• FFB3D/FB3D debugging (order and dtype patches)
• Remove unused skimage dependency
• Add aspire cli entry point
• Fix ImageArraySource and add working tutorial to test suite
• Minor doc updates
• Use nufft "many" interface in 3D calls
• Add isotropic noise estimator
• Separate save function into save_metedata and save_images
• Option to load numeric backend modules