First release of the python package `PySphereX`.
Features of this release include:
* Surface integral over the unit sphere
* 'Expansion' class that handles spherical harmonics expansions
* Convenience constructor to initialize `Expansion` object from gridded data
* Evaluation of `Expansion` object on an arbitrary grid
* Angular power spectrum and total power
* Normalization of `Expansion` object
* Algebraic operations: Addition, subtraction, overlap integral
* Unit tests for all features
* Example script + example data