Homogeneous Linear Diophantine Equations

This PR adds the ability to solve homogeneous linear Diophantine equations.
 
I converted python code found [here](https://github.com/sympy/sympy/pull/7241) to C++. These are the to-dos listed there.

* Implement solutions for inhomogeneous case
* Add more tests
* Find solutions in negative integers if possible

These can be implemented in separate PRs. I skimmed through the paper but I don't remember why I put the  last one. Let's think about that after this PR is merged.