feat: allow omitting of dates from date ranges

[Aparaxium]

Allows the user to omit dates in date ranges using the logic:

#let daterange(start, end) = {
    if start != none and end != none [
        #start #sym.dash.en #end
    ]
    if start == none and end != none [
        #end
    ]
    if start != none and end == none [
        #start #sym.dash.en Present
    ]
}