Ambiguous struct value always passed by reference

[diamondburned]

When #26 was implemented, all struct types now keep a Go pointer field in it.
This means that, no matter how the Go struct value is transferred around, the
actual C value is always passed by reference. This can be very confusing for
some Go code.

The workaround is probably just to add a piece of documentation into every
single generated record struct to clarify this. The caller is responsible for
calling the Copy() method, if there is one.

[diamondburned]

Fixed with a comment on every record struct.