Track: CGGTTS measurements

CGGTTS measurements (referred to as tracks) are Common View realizations.

Two classes of measurement exist:

CommonViewClass::Single
CommonViewClass::Multiple - actually Dual frequency

A track comprises several data fields, refer to the crate official documentation for their definition.

let first = cggtts.tracks.first()
    .unwrap();
assert_eq!(first.elevation, 1E-9);
assert_eq!(first.azimuth, 1E-10);

Follows BIPM tracking recommendations:

assert_eq!(first.follows_bipm_specs(), true);