Support for sparse algebra and bulk constraint addition

Hi,

I integrated and heavily modified PuLP for my program GridCal.
Doing so, I made this [module](https://github.com/SanPen/GridCal/blob/master/src/GridCal/ThirdParty/pulp/pulp_extra.py) to handle sparse algebra. This way I can model algebraic equations (`A @ b < c`) with no for-loops in the program itself.

This feature is something these modelling frameworks often lack and they make models far more maintainable.