[Twig] CVA - Rework implementation + documentation

[smnandre]

Q	A
Bug fix?	no
New feature?	no
Issues	..
License	MIT

Try another implementation + add some tests.

Updated/added a lot of documentation in the CVA class.

All tests are green but i'm not 100% sure this made no change at all :|

@WebMamba I let you decide what you want to do with it (i needed a class to test some things :) ) .. really open to any choice :)

@kbond that does not include your modifications i think :|