Add Calibre and Kindle meta in Compat doc

[JayPanoz]

@HadrienGardeur Could you please review the Calibre’s title_sort addition starting line 118? I’ve found lots of conflicting information so I’m not sure everything is covered there.

[JayPanoz]

OK, as per Hadrien’s suggestion, pinging @kovidgoyal for this title_sort addition: https://github.com/readium/readium-css/blob/9e2408c0f58bee08ae395843664a70563d26803d/docs/CSS21-epub_compat.md#title-sort

Is this correct? Are we missing something?

Context: We will support such useful metadata in Readium 2 so we’d better get details right. The dedicated issue is open here: readium/architecture#70

[kovidgoyal]

Yes, that is correct. Note that in calibre series_index can be a floating point number with up to two digits of precision, for example 1.01 and the values of zero and negative numbers are allowed.

Rating in calibre is always an integer between 0 and 10, where 0 is unrated and 10 is 100% (displayed as five stars in calibre). In theory odd numbers such as 1 and 3 could display as half stars, but that is not currently implemented.

[JayPanoz]

@kovidgoyal Thanks! Very much appreciated.

I’ll add those extra details ASAP tomorrow morning.