Add lookup function for census block groups

[mhweber]

Create an sc_get_block groups function to return block groups touching a catchment (watershed? riparian buffer?) and vice-versa? simply build staged lookup table or generate dynamically? We may want to have as a AOI in the API rather than a package function

[jbousquin]

Not sure how far into this you are but some base urls I've used in python in the past that might be useful starting place:
"https://tigerweb.geo.census.gov/arcgis/rest/services/TIGERweb/Tracts_Blocks/MapServer"
from tigris:
"https://www2.census.gov/geo/tiger/GENZ/shp/cb__<state_fip>_bg_500k.zip"
"https://www2.census.gov/geo/tiger/TIGER/BG/"

[mhweber]

@jbousquin - thanks for the urls - hope to work on this over coming month