nlutmap - map to LUTs of different sizes

    nlutmap [options] [selection]

This pass uses successive calls to 'abc' to map to an architecture. That
provides a small number of differently sized LUTs.

    -luts N_1,N_2,N_3,...
        The number of LUTs with 1, 2, 3, ... inputs that are
        available in the target architecture.

        Create an error if not all logic can be mapped

Excess logic that does not fit into the specified LUTs is mapped back
to generic logic gates ($_AND_, etc.).