TODO

- GPUs

- Test BCB convolution for odd-size grid

- Concatenating explicit matrices

- Make space data shape vs. pixel shape cleaner! (or just keep track better)
- Broadcasting to full data shape, including channels and stokes

- Joint modeling of multiple data sets!!!

- Mask as part of VisibilitySpace

- All TODOs in code

- Documentation!!!

- Clean up unit tests, split into more manageable files


- Re-organize sub-modules ('spaces', 'util'?)
- Move misc operators and CSR matrices to their own files


- Use 2F1 series for all deflection computations

- Regularization operators

- Solver framework

- scikit-sparse for Cholesky and solvers

- Duck typing everywhere... quit typechecking function args!

- Clean up dependencies in setup.py
- Merge all c code into one backend module?