TAJO-957: ROUND should be support INT parameter. (Mai Hai Thanh via hyunsik)
TAJO-978: RoundFloat8 should return Float8Datum type. (Hyoungjun Kim via hyunsik)

Closes #96
TAJO-979: Dividing float value by zero should throw "Divide by zero Exception" (Hyoungjun Kim via hyunsik)

Closes #100