add -d / --dem_file option to input DEM file as an alternative for --bbox option.
add dem2bbox() to grab bbox from existing DEM file
adjust download_waterMask() that: if DEM file is input, put downloaded water body mask file to the same directory as the DEM file.
adjust the default water mask file in radar coordinates that:
1. in the same directory as the input lat/lon files
2. named as "waterMask.rdr" instead of "swbdLat_*.wbd.rdr"
add example docstring and update parser description.
Zhang Yunjun
Eric Gurrola