Allow `β` element to accept lists as arguments

[Little Monkey]

Description

Allow it to convert to base 10 from an arbitrary list base, like what τ does in reverse.

Details

For example, ⟨ `a` | `dd` | `c` | `a` ⟩ ⟨ `a` | `c` | `dd` ⟩ β would return 21.