- rename definition in swagger from `Image` to `ImageInspect` to match the go type
- improve (or add) documentation for various fields
- move example values in-line in the "definitions" section
- remove the `required` fields from `ImageInspect`, as the type is only used as
response type (not to make requests).
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>