Add Possible.Math re-open

[Victor-Ochoa]

https://github.com/possible-brazil/Possible.Math.Finance

@thangchung e @ngohungphuc
Good morning, how are you?
    This project is the conversion of a class of financial calculations that comes from excel, it was a big problem in a project of mine where I had to accomplish it in .net framework because there is no such class in the .net core and Microsoft does not have the plan to convert.
    However simple it is, calculations are complex and used in financial and banking systems around the world.
    This class enables these systems to be made by in.Net Core.