Added demo parameter to docu_login, which indicates whether to use the DocuSign demo API.
Added docu_list_envelopes, which retreives envelopes since a specified date.
Added docu_envelope_status, which retreives an envelope's status.
Added example for docu_download.
Added a NEWS.md file to track changes to the package.
Added docu_templates, which retreives an accounts templates.
Added docu_download, which downloads signed documents.