Use-cases for linear algebra

[altavir]

Linear algebra has a lot of applications. We obviously need to cover the most used ones. Current implementation allows for vector operation inside single vector space (without concern for actual space elements), but does not work for operations outside of vector space like multiplication of vector by matrix. So please write typical use cases.

Note, that we do not need vector spaces for a lot of things like linear equations. We have a Point class which is similar to Vector but does not bring vector space with it. Also matrices are currently forming they own space. Do we really need it, or we can work with some structure without summing rules?