Implement TWIT_get and TWIT_post helpers

[hadley]

I'd suggest adding helpers that looked something like this:

TWIT_get <- function(query, param, ..., token = NULL) {
  old <- options(scipen = 15)
  on.exit(options(old))
  
  token <- check_token(token)
  url <- make_url(query = query, param = param)
  httr::GET(url, ..., token)
}

This logic is currently spread over many functions. I suspect these functions should probably also incorporate warn_for_twitter_status() and from_js() so that API errors are also handled in one place.

[hadley]

And warn_for_twitter_status() should be replaced with stop_for_twitter_status().

[hadley]

Closing, since this is now done.