[Agda] Refectoring Builtins

[Simon Foster]

Hi,

What's the best place to store new builtin definitions? At the moment  
I've got them as an additional field in TCState, which seems to be the  
easiest. I've then altered resetState to make this new field  
persistent between reloads, as I notice you're already doing with  
command-line options - is this acceptable?

I'll also need an additional field to store external tool functions  
(something like [[String] -> Term -> TCM Term]).

Thanks,

-Si.