- change Option return type for NcResult when appropriate.
- make NcDirect constructors return NcResult.
- rename NcError::new() to with_msg() and simplify new().
- refactor examples:
- rename direct-image.rs to direct-image-c.rs
- recreate using rust methods, as direct-image-rust.rs
- differentiate more throughly between both styles.
- remove the sys namespace on both examples.
