Update CreateChangeCompletionStream to return the entire response upon
stream completion. Renamed HandleDelayedResponse to
HandleDelayedContent, which no longer returns the content.
Removes the need wrapping HandleDelayedContent in an immediately invoked
function and the passing of the completed response over a channel. Also
allows us to better handle the case of partial a response.
Add new SetStructDefaults function to handle the "defaults" struct tag.
Only works on struct fields which are pointers (in order to be able to
distinguish between not set (nil) and zero values). So, the Config
struct has been updated to use pointer fields and we now need to
dereference those pointers to use them.
Matt Low