More iUniform possibilitys

[Hendiadyoin1]

It would be nice if you would have more ways to restrict the iUniform varialbles.

My ideas are:

• non-linear step modifiers (ie. exponential base x)
• list selects
• boolean support

could be that for some of these there are other ways to do them, or that the glsl standard does not allow them though

[Malacath-92]

This is not really a question of what GLSL supports (or webgl in our case) but just of what the gui we use supports. I think the suggestions you make are quite useful but we'd need to fork dat.gui to add some of them ourselves. I'm not sure how feasible that would be, but I'll look into it.