acs_transform: Parse raw data, calculate new varibles, export as csv
In austensen/acssf: Download ACS Summary File Data and Build Database

This function parses the data downloded by acs_download() and creates a csv file for the selected parameters.

1	acs_transform(year, span, geo, sum_levels, keep_vars, acs_dir = ".", .f = NULL)

`year`	[integer(1)]: The year of the desired ACS sample. For example, use 2010 for the 2010 1-year ACS or the 2006-2010 5-yer ACS.
`span`	[integer(1)]: The span of years for ACS estimates. ACS contains 1-, 3-, and 5-year surveys.
`geo`	[`charater(1)`]: The 2-letter state abbreviation or 2-digit FIPS code for the state for which data will be downloaded. For geogrpahies that do not nest within states, use `"us"`.
`sum_levels`	[`character`]: The Census Bureau codes for the summary level to include in the table. (eg. "010" = United States) For full list see https://factfinder.census.gov/help/en/summary_level_code_list.htm.
`keep_vars`	[`character`]: A character vector of ACS variable codes to be included in the output table, using the format `"b25003_001"`.
`acs_dir`	[`character(1)`]: The root directory in which all the ACS data has been downloaded with `acs_download()`. Defaults to current working directory.
`.f`	A function or formula to be passed to `purrr::as_mapper()`. The function must take a single dataframe as the only argument, and return a single dataframe. If a function, it is used as is. If a formula, e.g. `~ .x + 2`, it is converted to a function. There are three ways to refer to the arguments: For a single argument function, use `.` * For a two argument function, use `.x` and `.y` * For more arguments, use `..1`, `..2`, `..3` etc This syntax allows you to create very compact anonymous functions.