Chained transformations

[MichaelClerx]

It should be quite easy to add a Transformation class that takes 2 or more transformations as constructor arguments, and then just applies them all.

Useful if, for example, you want to apply some kind of transformation to change the shape of the objective function (e.g. a log transform), followed by a transformation to change the scaling (e.g. project onto the unit cube)