Added the ModelBuilder class and updated the VariableSwitch to use a new model based on the ModelBuilder.
Update README.md
Clean up the ModelBuilder slightly.
Change the signature of torchPart to be a curried function that takes a height parameter (how tall to generate the torch) and a PartBuilder to build the torch.  This allows for a torch height to be specified and the resulting unary function to be passed to the addPart function of ModelBuilder to add a torch of the given height.
Updated the Variable Switch recipe and make it so that the variable switch drops when the block it is attached to is removed.