Some functions may return a URL (for example etrd_option_chain)
that requires a further GET request. This function can return the contents.
The access token and etrade credentials must be explicitly passed.
Access tokens are created using
etrd_auth_access_token. This entry is not required because
the output is saved and retrieved from R options automatically.
etrade_cred
The output created from
etrd_auth_credentials when a valid ETRADE key and secret have
been passed. This entry is not required because the output is saved and
retrieved from R options automatically.