Get total Facebook ad spending per day and as a rolling average

Usage

cc_get_fb_ads_totals_by_day(
  ads_df = NULL,
  start_date = NULL,
  end_date = NULL,
  before = 3,
  after = 3
)

ads_df: A data frame, such as the one retrieved with `cc_get_fb_ads()`
start_date: Defaults to 91 days before today
end_date: Defaults to yesterday.
before: Defaults to 3. Days to keep before the given day for calculating rolling averages.
after: Defaults to 3. Days to keep after the given day for calculating rolling averages.