def agreement_document_file(agreement_id, document_id, file_path=nil)
     response = Echochamber::Request.agreement_document_file(token, agreement_id, document_id)
     unless file_path.nil?
       file = File.new(file_path, 'wb')
       file.write(response)
       file.close
     end
     response
   end
def agreement_document_file(agreement_id, document_id, file_path=nil)
     response = Echochamber::Request.agreement_document_file(token, agreement_id, document_id)
     unless file_path.nil?
       file = File.new(file_path, 'wb')
       file.write(response)
       file.close
     end
     response
   end
Retrieve a document file from an agreement

 @param agreement_id [String]  (REQUIRED)
 @param document_id [String]  (REQUIRED)
 @param file_path [String] File path to save the document.  If no file path is given, nothing is saved to disk.
 @return [String] Raw bytes from document file