Return an empty repostory backed by an in-memory event-store.

true if sub is either nil, equal to x, or a recursive subcollection of x.

If sub is a sequential collection of size N the first N elements of x are tested. If sub is a map every value in sub is tested with the corresponding value in x. If sub is a set every key in sub should exist in x.

Examples:

(sub? nil
      {:anything :at-all})
(sub? [:a :b]
      [:a :b :c])
(not (sub? [:a :b :c]
           [:a :b]))
(sub? {:a [1 2 3]}
      {:a [1 2 3 4] :b 2})
(sub? {:a [1 nil 3]}
      {:a [1 2 3 4] :b 2})
(not (sub? {:a [1 2 3 4]}
           {:a [1 2 3] :b 2}))
(sub? #{:a}
      {:a 1 :b 2})
(sub? #{:a}
      #{:a :b})
(not (sub? #{:a :c}
           #{:a :b}))
(sub? :something
      :something)
(sub? [:1 :2 :3]
      (list :1 :2 :3))
(sub? [:1 :2]
      (list :1 :2 :3))
(sub? (list :1 :2 :3)
      [:1 :2 :3])
(not (sub? (list nil 2)
           [:1 :2 :3]))