Updated to v1.5.3

v1.5.0 Added Metric option suggested by TimU

v1.5.1 Corrected US Gallons to Liters conversion (was previously using value from Liters to British Gallons)

v1.5.2 Converted most cell references to Named References to increase readability of functions.

v1.5.3 Split Imperial into US and Imperial, since US uses a different gallon from Imperial. 1 US gal = 128 fl oz; 1 Imperial gal = 160 fl oz