Re: Concepts syntax and interfaces - declarative vs procedural

[GULPF]

IMO there are good reasons for the current syntax. What if < is implemented 
with a template? What if it has a third argument with a default value? What if 
only `<`(x, y: int): bool` exists, but there's a converter for `T` -> `int`? 
Since Nim has so much flexibility in how to implement things, concepts needs to 
be flexible as well.