Assertable extensibility

[mausch]

Like http://hackage.haskell.org/packages/archive/HUnit/1.2.5.1/doc/html/Test-HUnit-Base.html#g:3 , but obviously instead of a typeclass use a dictionary of Type -> ((unit -> 'a) -> (unit -> unit)) and reflection. Or use statically resolved inline classes: https://github.com/gmpl/FsControl

This would enable a simpler syntax for those cases when you only want to check equality or some boolean result.