2 - requirements around conformance

Section 2 includes:

> A conforming implementation of C# is permitted to provide additional types, values, objects, properties, and methods beyond those described in this International Standard, provided they do not alter the behavior of any strictly conforming program.

This is probably stricter than we want... almost any change can alter the behavior of a strictly conforming program in some ways. Consider adding an instance method to `Delegate` - then anyone creating an _extension_ method on `Object` with the same name and then calling it on a `Delegate` would find that the instance method was called instead of their extension method.

Basically I think this is a matter of finding suitable wording once we've decided what level of breakage is acceptable.