Support template functions

[atilaneves]

It should be possible to write:

double foo(T...)(T args) {
}

And have that wrapped by an Excel function that takes, say, 32 XLOPER12* and forwards accordingly, checking which ones are xlTypeMissing

[UplinkCoder]

If you are going to do this, I advise using a lot of static asserts :)

[atilaneves]

@UplinkCoder Don't I always anyway? ;)

[UplinkCoder]

Ah right .... you have your own concepts.
... Preaching to the choir I guess.