ISO/IEC 23091-4 should be changed to ISO/IEC 23091-2

[wantehchang]

In Version 1.0.0 with Errata 1, there are five occurrences of "ISO/IEC 23091-4". Four are in 6.4.2. Color config semantics, and one is in Bibliography.

Here is an example,

color_primaries is an integer that is defined by the “Color primaries” section of ISO/IEC 23091-4/ITU-T H.273.

The "-4" in "ISO/IEC 23091-4" is a typo because ITU-T H.273 is technically aligned with ISO/IEC 23091-2, not ISO/IEC 23091-4.

"ISO/IEC 23091-4" should be changed to "ISO/IEC 23091-2".

[y-guyon]

Suggested change: #344