* Semantics Enhancements:
* adds 142 streamflow characteristics of the 171 inventoried by [Olden and Poff (2003)](https://doi.org/10.1002/rra.700)
* Functionality Enhancements:
* adds possibility to select specific years where to calculate the SFCs using the keyword argument `years`
* adds gathering functions for each flow category (`magnitude`, `frequency`, `timing`, `duration`, `rate_change`) and for all SFCs (`everything`)
* Algorithm Enhancements:
* adds single-sourcing package version
* changes default array orientation
* changes the degrees of freedom to n-1 in calculation of std (breaking backwards compatibility)