Feature request: Clone a FunctionRegistry with exclusions

[gibson042]

The FunctionRegistry extend method can be used to create a new registry that has all the functions of the context registry plus provided additions. But it should also be possible to create a new registry that has all the functions of the context except provided exclusions. This can be used to filter out e.g. functions with known non-linear performance:

FunctionRegistry defaultRegistry = FunctionRegistry.defaultRegistry();
FunctionRegistry saferDefaultRegistry = defaultRegistry.extendWithout("merge", "sort", "sort_by");