Allow conversion to a unit list

[ben-cohen]

GNU Units allows you to convert to a sum of two or more units separated by semicolons, called a "unit list". It returns the largest whole number of the first unit, and then uses the next unit for the remainder, and so on:

You have: 7 meters
You want: ft;in
        22 ft + 11.590551 in
You have: 7m
You want: yard ; foot ; inch
        7 yard + 1 foot + 11.590551 inch

In Units, I expected the same result for the inputs above, but instead it gives the error "Unit ';' is unknown."

It would also be useful to have a button to enter ;.

[buttercookie42]

v1.2 of my fork can now do this.