Macro mqtt_packet::build_enum

macro_rules! build_enum {
    (@accum (1, $name:ident { $([$($doc:expr,)*] $key:ident = $value:expr),* })) => { ... };
    ($name:ident {
      $($key:ident = $value:expr),*
  }) => { ... };
}

Generates a public enum with the following traits implemented:

• From<T> for u8
• TryFrom<u8> for T