Allow tuples as input for `%`, but disallow them in the generic type of the `%` proc that accepts openArrays.
Additionally addedthe isNamedTuple(T) proc. Can instead also be imported from std/typetraits, but ig dependencies should be kept to a minimum.

added additional conversion info to the proc, copied it straight from an earlier issue

Forgot to change parts of the copied code from jsonutils.

Something like proc myproc[T: object|tuple](o:T): void = ...
might not accept the tuple properly even though it's supposed to, such that:
myproc(mytup) doesn't work. 
Idk if that was the actual problem here, but just to be sure, I changed the respective functions.