CNRFC seasonal trend (product 7, 9) CSV

[narlesky]

Generate query URL with the following to access CSV-formatted data and produce methods to download and parsing seasonal and water year trend data

https://www.cnrfc.noaa.gov/ensembleProductTabular.php?id=FOLC1&prodID=7&year=2021

cnrfc_id = 'FOLC1'
product_id = 7
year = 2021
url = f'https://www.cnrfc.noaa.gov/ensembleProductTabularCsv.php?id={cnrfc_id}&prodID={product_id}&year={year}'

Would be beneficial to have utility for determining which forecast locations include this product as well!

[narlesky]

Closed by #57 and earlier