User-facing API

[klamike]

Currently the functionality exists but it is rather convoluted to use

L2ODLL.jl/test/runtests.jl

Lines 92 to 100 in fe32671

	blp_cache = L2ODLL.build_cache(m, L2ODLL.BoundDecomposition(m));
	blp_y_pred = randn_like(L2ODLL.get_y(blp_cache));
	dobj1 = blp_cache.dll_layer(blp_y_pred, param_value)
	dobj, dobj_wrt_y = DifferentiationInterface.value_and_gradient(
	(y,p) ->blp_cache.dll_layer(L2ODLL.unflatten_y(y, L2ODLL.y_shape(blp_cache)),p),
	DifferentiationInterface.AutoForwardDiff(),
	L2ODLL.flatten_y(blp_y_pred), DifferentiationInterface.Constant(param_value)
	)
	dobj_wrt_y = L2ODLL.unflatten_y(dobj_wrt_y, L2ODLL.y_shape(blp_cache))