No need for reflection.
Ensure response body is closed.
Return proper errors when requests fail.
Add app authentication.

Ensure response bodies are closed.
New API method: GetItemByExternalID
Add fields and values for Item.
Get and create comments.
Create and update item.
Check err before adding headers.
Refactor requests with JSON payload.
More elaborate example.
Split into multiple files.
Updated README.
Rename FooID => FooId.