Macro bit_struct::enums

macro_rules! enums {
    ($($(#[doc = $struct_doc : expr]) * $(#[derive($($struct_der : ident), +)]) ?
   $enum_vis : vis $name : ident $(($enum_default : ident)) ?
   {
       $(#[doc = $fst_field_doc : expr]) * $fst_field : ident
       $(, $(#[doc = $field_doc : expr]) * $field : ident) * $(,) ?
   }) +) => { ... };
}

Create enums which have convenient TryFrom/From implementations. This makes using them with the bit_struct macro much easier.