Macro assert_segments

macro_rules! assert_segments {
    ($string:expr, [$($segment:tt),+]) => { ... };
    (@verify_segment $seg:expr, { $($field:ident => $value:tt),* }) => { ... };
    (@check_field $seg:expr, len, $expected:expr) => { ... };
    (@check_field $seg:expr, txt, $expected:expr) => { ... };
    (@check_field $seg:expr, sgr, $expected:literal) => { ... };
    (@check_field $seg:expr, sgr, None) => { ... };
    (@check_field $seg:expr, rst, $expected:literal) => { ... };
    (@check_field $seg:expr, rst, None) => { ... };
}