Function Definition documentation out-of-date

[jurgenvinju]

Describe the bug

https://www.rascal-mpl.org/docs/Rascal/Declarations/Function/

This document:

• still separates functions with and without patterns, while in fact there are only functions with patterns.
• does not clearly document keyword parameters with default values
• does not clearly document overloading and dynamic dispatch
• does not explain the interaction over function overloading with constructors
• does not explain the interaction of function overloading with module extend

I write it here so I will not forget about this.

[toinehartman]

Addition w.r.t. undocumented features; it also does not make any mention of when clauses. They are never mentioned in the documentation I believe - also not for switch cases.