Reciprocalspaceship

- Add utility method for computing phase restrictions
- Bug fixes to improve handling of the `MultiIndex` in `DataSet` built-in methods (6)
- Add append/concat methods to `DataSet` and `rs` that preserve metadata/attributes
- Argument to account for centering in epsilon calculation (7)
- Improve performance of `hkl_is_absent()` and `is_centric()` through calls to `gemmi` vectorized functions
- Add methods for binning reflections (e.g. by resolution: 9)
- Most importantly: `rs` now has a logo... 1/:rocket:

Bug Fix:
- Fix output of rs.mtzdump commandline tool

- Release reciprocalspaceship on PyPI

- Completed documentation including User Guide, API Reference, and For Developers sections
- Support for reading/writing unmerged MTZ files by mapping indices based on M/ISYM flag
- Support for converting anomalous data between 1-column and 2-column format
- Added inference methods for MTZ dtypes
- More complete tests for crystallographic methods over all supported spacegroups

This is the first public release of `reciprocalspaceship`.

Updates since the last release:
- Sphinx documentation with usage examples
- compatibility with Pandas 1.0
- removal of unnecessary utility functions that were specific to Hekstra lab projects
- Change `Crystal` and `CrystalSeries` class names to `DataSet` and `DataSeries`
- GitHub Actions for CI and publishing of documentation to gh-pages branch
- Improved unit test coverage and report from codecov.io

Initial release of reciprocalspaceship, containing a Crystal object for representing reflection tables using Pandas Dataframes.

Features:
- Read and write MTZ files
- Read HKL files from Precognition (Laue diffraction processing software)
- Custom dtypes for representing crystallographic data (intensities, structure factor amplitudes, etc.)