upgo_scrape_cl: Function to scrape Craigslist listings
In UPGo-McGill/upgo: Utility Functions for UPGo Lab Members

upgo_scrape_cl scrapes all data from Craigslist rental listings in a given city.

upgo_scrape_cl(
  city,
  old_results = NULL,
  old_results_add = FALSE,
  recovery = FALSE,
  proxies = NULL,
  quiet = FALSE
)

`city`	A character scalar indicating the city to scrape. It must correspond to the domain prefix used for a city's Craigslist site (e.g. "sfbay" for the San Francisco Bay area).
`old_results`	A data frame. If the output of a previous run of `upgo_scrape_cl` is supplied, listings previously scraped will be incorporated into the new results.
`old_results_add`	A logical scalar. Should the function add old results to the table, or skip them (default)?
`recovery`	A logical vector. Should the function attempt to recover results from a previous, unsuccessful function call?
`proxies`	Character vector of IPs to use for proxy connections.
`quiet`	A logical vector. Should the function execute quietly, or should it return status updates throughout the function (default)?