Project dependencies

- Added `org.clojure/tools.namespace` and
  `org.clojure/math.combinatorics`.

Signed-off-by: giorgio-v <giorgio@refactor.it>
Better assoc-and-cons-invariant

Signed-off-by: giorgio-v <giorgio@refactor.it>
`sum` reimplementation

See inline comments for more context.

Signed-off-by: giorgio-v <giorgio@refactor.it>
Knapsack problem

To be continued?

Signed-off-by: giorgio-v <giorgio@refactor.it>