Add eConvOp to complement eBinOp and eCmpOp.
Add eConvOp to complement eBinOp and eCmpOp.

HIPERFIT/futhark,diku-dk/futhark,diku-dk/futhark,diku-dk/futhark,HIPERFIT/futhark,diku-dk/futhark,HIPERFIT/futhark,diku-dk/futhark