Make the cpp! macro a real proc macro

[ogoffart]

It's still using the old derive marco hack.

Having a real proc macro will also make the rust! better as we won't need an unique name in there, and we will not have to increase the recursion depth.

[luke-titley]

Are there any more thoughts on this ? Any plans to make this happen ?

[ogoffart]

I've been wanting to do that for a long time, but never got around to do it.
The current system is working well enough for me so i didn't get the incentive to change work on it.

If you want to give it a try, it should be pretty easy to do.