Further cleanup/regularisation of Callback_wrapper classes and trampolines
Contains two commits:
Callback_wrapper:: move trampolines and make_smob to Callbacks class
Make Callback_wrapper a class template
Templating Callback_wrapper on the wrapped argument list avoids a lot
of code repetition.
Diff:
Passes make, make check and a full make doc.
Patch on countdown for May 6th
Patch counted down - please push