[Closed] Type hierarchy for vectors and matrices

[WhiteBlackGoose]

Here we should design the API and behaviour of linear algebra for the project.

1. What do we want?

Which types do we want? Vector, Matrix, Tensor? Or do we only need Vector and Matrix?

2. How should they inherit?

Vector : Matrix
Matrix : Entity

Vector : Matrix
Matrix : Tensor
Tensor : Entity

Vector : Entity
Matrix : Entity
Tensor : Entity // depends on whether we need Tensor

Vector : Entity, IVector
Matrix : Entity, IMatrix
Tensor : Entity, ITensor // depends on whether we need Tensor

3. Operations on them

When being part of an expression, should it keep elementwise operations only, according to #168 or not?

[WhiteBlackGoose]

Alright, the solution is: no vector, no tensor. Only matrix. All operations accordingly. Track the PR.