Products are looked up by product id (store-prefixed, as returned in
product results), by the retailer's own item numbers (skus with store, as
printed on its receipts), or by name (query). ingredients_incomplete marks
an ingredient list on record that is cut short, which cannot show that an
ingredient is absent. Results carry a note that nutrition and ingredients
are for information only. Each product returned costs one credit.

Args:
    query: product name words, e.g. "kellogg's corn flakes".
    product_ids: e.g. ["tesco:300793546", "dunnes:100873410"], up to 50.
    skus: the store's own item numbers, e.g. ["100873410"], up to 50;
        needs store. An Aldi article number can return several variants.
    store: aldi, tesco, supervalu or dunnes: required with skus, narrows a
        query; leave out for all four.
    limit: most products to return for a query (default 5, max 50).