`UnsafeFunctionPointer::Args` as a convienence.

[JCBurnside]

Is your feature request related to a problem? Please describe.
I am trying to add additional wrapping around engine.get_function to make a jit runtime that would be reusable.

fn get_function<F:UnsafeFunctionPointer>(&self, name:&str, args:...) {
    let function = //gets function
    function.call(args)
}

Describe the solution you'd like
Just simply add an associated type that is a tuple of all the args in the UnsafeFunctionPointer

Describe possible drawbacks to your solution
I don't see one?

Describe alternatives you've considered
essentially cloning the UnsafeFunctionPointer type and adding it myself and making a blanket implementation to map it.

Additional context

[JCBurnside]

Just realized that your call function is also inconsistent with the nightly fn_traits feature see here so not sure what I want is possible with the current api unless an alternate means of calling it as like call_tuple added to JitFunction as well.

[TheDan64]

I'm not entirely sure if this makes sense to have in inkwell itself, but I'm open to ideas