Added
- Adds support for masking variables in their definition, issue 59 [benkrikler](https://github.com/benkrikler)
- Adds several constants for variable expressions, issue 21 [benkrikler](https://github.com/benkrikler)
- Added this changelog [benkrikler](https://github.com/benkrikler)
Changed
- Use `pandas.groupby(..).counts()` to make binned dataframes, issue 51 [benkrikler](https://github.com/benkrikler)
Removed