Loads plain-text data (e.g. CSV, TSV) data from a Dropbox
non-public folder. To download data from a Drobpox Public
folder simply use read.table, giving the public URL
as the file name.To download data using source_DropboxData you will
need (a) the file's name and (b) its Dropbox key. The key
can be found by clicking "Share Link". The key will then be
listed as part of the URL directly after
"https://www.dropbox.com/s/" and before the file name.
From the source_url documentation: "If a SHA-1 hash is
specified with the sha1 argument, then this function will
check the SHA-1 hash of the downloaded file to make sure it
matches the expected value, and throw an error if it does
not match. If the SHA-1 hash is not specified, it will
print a message displaying the hash of the downloaded file.
The purpose of this is to improve security when running
remotely-hosted code; if you have a hash of the file, you
can be sure that it has not changed."