TODO docs tweak.
Organized code in Uize.String to better optimize for size.
Minor tweak.
Created a calculator widget abstract class so that the newer Uize.Widgets.Calculator.Widget class doesn't have to inherit a dependency on Uize.Widget.Button (added a buttonWidgetClass static property to the abstract class and made Uize.Widget.Calculator set it to Uize.Widget.Button)
The Uize.String.toCamel method is too esoteric and infrequently used to be adding weight to the Uize.String module, so it's now in a dedicated Uize.String.Camel module, and this module can eventually also get a method for converting from camelCased strings back to some other delimiter.