[Feature Request] Allow modulus operator in requires

[AlanRosenthal]

I would like to enforce this requirement: Range: 0x0002 to 0xFFFE; only even values are valid

I was envisioning something like this:

    [requires: 0x0002 <= this <= 0xFFFE]
    [requires: this % 2 == 0]

[reventlov]

This would be covered by #41