Draft proposal for mixin template intermediary storage

[rikki cattermole]

I think you have caught on to something that I played a little bit 
during BeerConf.

We need to make the compiler 'forget' certain template instantiations 
and with that, to not directly expose them outside of a mixin template 
body would be a good semantic to it.

I refer to them as a type function, because its a meta-function that 
operates on types. Its not quite types as first-class, but more of a 
reference to something in the AST that is a type.

It could be a possible solution to deadalnix's data structure problem 
with storage classes like const if it has the right hook.