function to stage NHD+ curated data

[aappling-usgs]

need column renaming, table merging, etc., as in https://github.com/USGS-CIDA/stream_metab_usa/tree/master/starter_files/data_scripts/stets_wieczorek

[aappling-usgs]

could also/alternatively think about using these published data from the EPA StreamCat dataset:

• web: http://www.epa.gov/national-aquatic-resource-surveys/streamcat
• metric list: ftp://newftp.epa.gov/EPADataCommons/ORD/NHDPlusLandscapeAttributes/StreamCat/Documentation/VariableList-QuickReference.html
• doc & data: ftp://newftp.epa.gov/EPADataCommons/ORD/NHDPlusLandscapeAttributes/StreamCat/WelcomePage.html
• paper: http://onlinelibrary.wiley.com/doi/10.1111/1752-1688.12372/abstract
• github: https://github.com/USEPA/StreamCat