iface - Dynamic dispatch on steroids

Nim methods no longer needed :).

• Go-like interfaces, implemented through fat pointers with vTbl. Allows implementing any interface for any (ref) type anywhere in the code.
• Works with default GC and --gc:orc.
• Works with all nim backends
• Works in VM (compile time or nimscript) Currently blocked by nim#16613 and nim#18613
• Works across DLL boundaries
• Provides compile time reflection API, which can be used for e.g. auto-generating proxy RPC callers/servers and such
• Allows generic interfaces. Example.

Usage:

import iface

iface Animal: # Define the interface
  proc say(): string

type
  Dog = ref object of RootRef # The Dog doesn't explicitly inherit Animal

proc say(d: Dog): string = "bark" # But it implements Animal interface by defining its procs
proc doSmth(a: Animal): string = a.say() # Here we're working with an animal
assert(doSmth(Dog()) == "bark") # Since Dog implements Animal it can be converted implcitly

Caveats:

• Converting to generic interfaces must be explicit, unlike example above. Above example should be rewritten as Dog().to(MyGenericAnimal[int])