Return Builder on set* Methods

[brianv0]

Better support for the builder pattern.

[brianv0]

Hi, I'm not sure if I got all the methods properly. In my limited tests, the output seems fine.

[idlsoft]

There are drawbacks to doing this if you ever want to implement some sort of class hierarchy for your structs.
A setter from a base class will return a base builder, making it impossible to use a setter from a subclass.

I know it's not a problem now, because there is no struct inheritance, but it'd be nice to have that option at some point.