Solutions for quadratic ternary forms implemented

Solutions for the ternary quadratic equation `ax^2 + by^2 + cz^2 + dxy + eyz + fyz = 0` implemented.
Currently uses the `descent()` method to find a non trivial solution.

###### Major TODOs:

- [ ] Implement a fast algorithm for `quadratic_congruence()`
- [ ] Verify the results with MAGMA's algorithm