As discussed in #177 hyper must support status code outside the
standard range for compatibility reasons.
BREAKING CHANGE: This removes unregistered status codes from the enum. Use
`FromPrimitive` methods to create them now. StatusCode and StatusClass can no
longer be casted to `u16`, use `ToPrimitive` methods now.
For example `status.to_u16().unwrap()` to get the status code number.
- Some stray deriving -> derive changes
- use::{mod} -> use::{self}
- fmt.write -> fmt.write_str
This does not catch the last case of fmt.write_str in the
Show impl of a Header Item. This will need to be changed
separately.
