Support prop behavior of nested method calls

[funkybob]

[funkybob]

In the current release it's a method, but will be invoked automagically when .use() resolves all the values.

With this change it will transparently be treated like it has @property before it. So trying to call it will result in an error (unless its return value is callable)

For the case in which I ran into this problem, there's a strong argument that it should never have been a 'public' property (i.e. SHOUTY_SNAKE_CASE) as it was only used to derive public properties.

[funkybob]

Having just run into this again, I'm going to merge this.