Fixed bugs/segfaults, added new algorithm, renamed misnamed function.

- A lot of mallocs were missing, causing segfaults.

- Fixed bugs in both BSGS.

- Tested another isomorphism algorithm.

- `eltseq_mono_BSGS` was wrongly named, because its output is on the
  dual-dual basis. Renamed to `eltseq_dual_BSGS`.

- Removed unused C code.