slackrUpload enables you upload files to Slack and
(optionally) post them to one or more channels (if channels is not empty).
slackr_upload(filename, title = basename(filename),
  initial_comment = basename(filename), channels = "",
  api_token = Sys.getenv("SLACK_API_TOKEN"))slackrUpload(filename, title = basename(filename),
  initial_comment = basename(filename), channels = "",
  api_token = Sys.getenv("SLACK_API_TOKEN"))
path to file
title on slack (optional - defaults to filename)
comment for file on slack (optional - defaults to filename)
slack.com channels to save to (optional)
full API token
httr response object from POST call (invisibly)