compound ket fn: split

split:
    description:
        split ket
        splits the ket into a superposition

        split["str"] ket
        splits the ket into a superposition, splitting on str

    examples:
        split |abcde>
            |a> + |b> + |c> + |d> + |e>

        split["d"] |abcdef>
            |abc> + |ef>

        split["g"] split["d"] |abcdefghij>
            |abc> + |ef> + |hij>

    see also:
        ssplit