unitsofmeasurement/unit-impl-se — pull request #28 by otaviojava (2014-09-16 23:15:18+00:00)
Title: add convert in add and subratc operations

Fix to in Quantity and convert before add or subtract, if these units are different, so now is possible:

Quantity day = AbstractQuantity.of(BigDecimal.ONE, SI.DAY);
Quantity hours = AbstractQuantity.of(BigDecimal.valueOf(12), SI.HOUR);
Quantity result = day.add(hours); //1.5 days

Quantity day = AbstractQuantity.of(BigDecimal.ONE, SI.DAY);
Quantity hour = day.to(SI.HOUR);//24 hours