Add co-author Reid Christianson; Add forward compatibility for Ld_Mixed

- Reid Christianson was the original developer of the Clean Water Optimization Tool when he was at the Center for Watershed Protection, and much of his work is built into this tool.
- Added forward compatibility for handling the outputs for "Low-Density Open" that will come with MMW v1.24 as described in #9 & #10. Although this implementation doesn't explicitly show the new mapping of "NLCD 21 Developed, Open Space", it will still give the correct answer.