In phasing: add support for differencemap, raar, and solvent-flipping algorithms.
Bug fixes in fit, wrapping
In kernels: bugfixes for phasing_dm1 and phasing_raar
In phasing: to complement new phasing algorithms, add optional argument for iterate() which allows specification of algorithm type. default is still a combination of hio/er
In phasing: speed ups along cpu path via numexpr, when available. unify coherence estimation methods in optimize_coherence. new def, gpu_prtf, which calculates the prtf using gpu for a big speedup when the number of reconstructions is large. big speed improvement in covar_results when doing a sparse calculation with a mask.

in io: include support for zipping outputs

in masking: new def, put_masked_pixels, which is a sort of inverse for take_masked_pixels

in conditioning, find some speedups on match_counts using numexpr

in gpu: dtype bug fixed in class common

in kernels, 2 new kernels to help with gpu_prtf