Support for non-standard unit scales (e.g. min, hour, days)

Not sure if this is something we want to add support for but currently units that don't use metric scales (e.g. min, hour, days, pounds, etc...) can't be represented in 9ML. There is an old example I found that includes a "scale" attribute in the Units element that enables this (the scale of minutes is 60, hours 3600, etc)