Flusspferd

I think how function params are treated needs a bit of tidying:

1. Optional params should use boost::optional, otherwise they are required
2. The number of params passed to a function must be at least as many as the required params
   • This would mean that (value x, optional< value > y, value z) would be invalid. If this is too hard to do, then just make the last param be optional too.
   • But you can pass more than the number of formal params, even if we can't access them (without using a call_context)- this is just how JS works
3. An (explicit or implicit) undefined should not be accepted for anything but a value typed param (See #127)