feat: Centers of Population

[ryanzomorrodi]

It would be nice to have Census Centers of Population integrated within this tigris. Since they exist at many different geographies, it could be an option on nation, states, counties, tracts, and block_groups or its own function with a geography argument like in tidycensus.

To add on to this, there could be a population weighted centroid function similar to spatialEco's wt.centroid, but implementing the Census methodology for calculating mean population weighted centroids for using longLat geometries. This function would perhaps be better housed within tidycensus because it would rely on population data from the census, but these ideas come from the same vain, so I wanted get thoughts first.

Census methodology for mean population weighted centroid: