Multi yr cumulative hydrograph
closes #8 (closed) by providing support for multiple years plotted on the cumulative hydrograph via the function. adds documented example of this functionality.
does automatic labeling via the legend for the various lines
example plot:
does this work? @shamshaw do you think there are options we are missing? right now the colors of the different years are fixed and pulled from the tab20
color-scheme (after the first line which is black) - should there be an option for users to provide their own set of colors for the individual year lines?
note: should be merged after !17 (merged)