Simplify Bounding-box

(From M. Taylor assessment [2022-01-17])

Sec 5: I feel that this section could be much simplified by just saying words to the effect: "A bounding box is of the form [lower_time, lower_spectral, upper_time, upper_spectral]". The complicated formulation in RFC7946 is necessitated by the fact that in GeoJSON there may be 2 or 3 coordinates and to avoid misunderstandings about the locus of a bbox edge between two points on a sphere (it's not a geodesic). Neither of these complicating factors applies to TFCat.

For the same reasons the algebraic description of what a line is in sec 3.1.1 could be elided as well.

Also I'm not exactly sure what the purpose of a bounding box is (in GeoJSON or TFCat). Is it an error for points in the scope of a bounding box to be outside of that box, or the bbox supposed to function as an additional clip rectangle?