libsemigroups::Perm:
- Member types:
  - value_type
  - container_type
- Static member functions:
  - identity() const
  - identity(size_t)
  - make(T&&)
  - make(std::initializer_list<value_type>&&)
- Member functions:
  - product_inplace(Transf const&, Transf const&)
  - inverse() const
