read_users: Read in openSNP user files from local storage.
Description
Beware, these tables can be large. Check your RAM before executing. Or
possibly read in a subset of the data. This function reads in the
whole kitten kaboodle.
Usage
read_users(name = NULL, id = NULL, path = NULL, ...)
If you specify a name or id, this function reads environment variables
written in the function download_users, and then searches against those
variables for the path to the file saved. Alternatively, you can supply
the path.