simplify ugen selection

[telephon]

Here is a suggestion of how to simplify the code for UGen selection. Let me know if that makes sense to you, I could help with other cases as well if you like it. I think it makes the library clearer to read. As a side-effect, we get rid of non-inlined functions (#51).

Of course the critical thing is testing the correctness of the changes, which would be something I can't properly do myself.