mkdb: new version table for tracking database changes.
fuel: usage/help stub
mkdb: s/version/versions. fix service date -> real
update: new module to update database schema
fuel new toDate, toTimestamp functions to convert date string to secs and back. fix up choose_fuel and get_fuel to use this. TODO: dates are 1 day out
fuel: s/toDate/to_date, s/toTimestamp/to_seconds. tidy up update_fuel
fuel: fix up `graph` to use new record structure
fuel fix for but #6. on start generate graphs for all vehicles. create index page with links for each graph
fuel: fix to_date to use locatime instead of gmtime (corrects for missing day...)