auto: new package for automatically wrapping Go functionality

[DeedleFake]

Currently, the primary way to access simple Go functions from WDTE is by providing a GoFunc to call. While this is nice as a low-level system, it would be quite useful to be able to just wrap existing Go functions without having to worry about perfectly matching the Func.Call() API. As such, a set of functions for automatically creating Funcs from existing Go structures would be quite useful.

As these are not technically required for the core functionality of WDTE, they should probably be in a separate package, such as wrap, fun, or simple. Maybe auto. Hmmm...

• func Func(name string, f interface{}) wdte.Func. Takes a name so that the frame can be subbed properly and a function. It uses reflection to create a wrapper around f that properly converts arguments passed from WDTE to requested types, automatically handling built-in types separately, and then converts the return value back as well. Might also support multiple return values.
• A variant of Func that lets the user specify how the arguments are handled, allowing for more complicated WDTE function signatures.
• The opposite of Func. A function that converts a wdte.Func to a Go function. Probably should work similarly to reflect.MakeFunc.