Add extract functions

[awunderground]

This PR adds create_county_extract() and create_place_extract() for TA requests.

For example, create_county_extract(fips = "11001", output_dir = "RMAPI_extract") creates a folder called RMAPI_extract/ and fills it with data subset to the specified FIPS.

It also reports back if any FIPS aren’t included in the data. For example, create_city_extract(fips = c("0103076", "abc", "def"), output_dir = "boom") returns the following message while creating the extract:

Queried FIPS in data: 0103076                                                                                                            
Queried FIPS not in data: abc, def