merge QuoInt and Rem into QuoRem.

[ericlagergren]

The GDA spec says Rem should fail in the same ways as QuoInt, which means literally in the same ways. Since this means we (effectively) cannot optimize QuoInt and Rem to reduce computations, for code clarity we should just merge the two into QuoRem.

[kentquirk]

Are you saying that you want to eliminate QuoInt and Rem entirely (which would be a breaking API change), or are you saying that the implementations of QuoInt and Rem should be converted to calls to QuoRem with a discarded value?

[ericlagergren]

@kentquirk Yeah, converted to calls to QuoRem with a discarded value.

Looking at #72, I'm not entirely sure this is still necessary. It's been 6 months since I created it so I'll have to reinvestigate. But yeah, no API breakage.