[TW-141] date-aliases

_David Patrick on 2013-08-09T22:24:22Z says:_

This feature request is for user-definable, .rc settable aliases for dates.

As an example, this would replace the existing due:someday variable (which currently resolves to 18/1/2038) with an rc entry

date-alias.someday=1/1/2020

but you could also define and use fun things like; later, eventually, soon, groundhogday and mybirthday

date-alias.later=+2weeks
date-alias.groundhogday='feb 02'