MassConcentrationUnit add ounces/gallon #947
Description
Is your feature request related to a problem? Please describe.
The unit does not seem to be available I am trying to convert from grams/mililiter to ounces/gallon.
Describe the solution you'd like
Implement the unit.
Describe alternatives you've considered
I tried implementing myself but I don't understand how, I've read the documentation but it wants me to create a new struct that inherits IQuantity implementing all methods from scratch.. I just want to extend MassConcentration.