Named arguments syntax with function definitions

[lukaszcz]

• Closes Function definitions in named arguments #2365
• Implements the syntax f@{x1 := def1; ...; xn := defn} and f@?{x1 := def1; ..; xn := defn}. Each definition inside the @{..} is an ordinary function definition. The @? version allows partial application (not all explicit named arguments need to be provided). This subsumes the old record creation syntax.

[jonaprieto]

This must be documented, please. I just saw this.