Implement NonZeroChar, like NonZeroU32

• Implemented of all char stable methods (most of forwarding)

Examples

use nonzero_char::NonZeroChar;

assert_eq!(NonZeroChar::new('a').unwrap(), 'a');
assert_eq!(NonZeroChar::new('\0'), None);

Null Pointer Optimization:

use nonzero_char::NonZeroChar;

assert_eq!(size_of::<NonZeroChar>(), size_of::<Option<NonZeroChar>>());