Variadic grouping

[JS]

Sometimes it's nice to be able to have groups of variadic 
parameters:

template t(T1..., T2...)
...

t!(a, b, c; d, e, f);

so that a,b,c are for T1 and d,e,f are for T2.

This can be done by making a symbol and breaking up a single 
variadic but is messy.

I doubt such a feature will ever get added but who knows...