Svmbir

- Changes default image size for 'fan' geometry
- Fixes C bug that could seg-fault for Large data sets
- Updates PIL resize constant in response to deprecation warning
- Updates to documentation

This release mainly adds support for fan beam geometry. (first for smbir!!)

- Relevant operators (`recon`, `project,` `backproject)` have 3 new arguments to specify the geometry: `geometry`, `dist_source_detector`, `magnification`.
- The operators default to parallel beam, so it's backwards compatible.
- New C code updates method of calculating matrix entries for easier generalization
- Corresponding updates to sphinx documentation, README and docstrings

Changes:
- Various updates to allow conda-forge packaging
- Pin numpy to 1.21.* in requirements to avoid mismatch error between build&run (224)
- Updates to setup.py to address warnings
- Corrected weight data type
- Include unit tests with package distribution
- Updated copyright statements
- Updates to documentation

Major bug fix in the parallelization of reconstruction: Previous versions could generate NaNs when the following conditions occurred together:
1. Large numbers of parallel threads are used (e.g., greater than 20 threads)
2. positivity=False is used
3. Small reconstruction is performed (e.g. 1 slice of size 256x256 or smaller)

New features:

- Sinogram sorting for improved performance when using Golden Section view sampling
- Adds install scripts
- Bug fix for setting num_threads
- Fixed version number setting technique
- Updated and reorganized args validation function
- Various bug fixes

What's new:

- Adds svmbir.backproject() operator
- Changes svmbir.project() argument order to (image,angles..), which includes a check so existing user code doesn't break
- Adds new regularization parameter sigma_p specific to proximal map mode, and also new auto_sigma_p() to compute default value
- Relevant updates to documentation