added history.csv endpoint
added XML endpoints
removed unnecessary empty attributes list
added status.rss endpoint
moved status field selection into timestamp_to_isofmt
added history.html endpoint
added home page with information
extracted function content_type/1
extracted function get_history/1
restructured resource for cleaner design
use built-in authorization method for submit endpoint
fixed generate_etag record field order
inserted additional newlines for readability
handle_submit: test for existence before writing object