moved files around to fit new structure

merged black scholes tests
removed files with duplicated functionality
OK. I'll rewrite to do that.

I think that design can be annoying in a library though. Maybe people won't use this code that way, but if you wanted to use this as a library then us having a class that forwards to different implementations can make it hard for someone to customise the functionality. I don't think what I was doing made it any easier though.

Interesting article on scala type classes and that problem: http://danielwestheide.com/blog/2013/02/06/the-neophytes-guide-to-scala-part-12-type-classes.html

I don't think we need it here but I'm still not sure about the design here. Maybe it will become clearer with a few more examples. For now I'll change it to a single Valuer class.