make EbmlElement::HeadSize private

[robUx4]

The Head size is rarely needed and may be 0 depending on writing filter.

Draft on top of #255

[mbunkus]

Hard no from me. mkvpropedit & the header editor both need to know the head size in order to determine where to place things. Sometimes they even have to expand the head size (by making the size field one byte larger the the minimum size) if they have to replace an existing element with an element exactly one byte smaller (meaning they cannot use an EbmlVoid there).

[robUx4]

to determine where to place things.

There's GetDataStart() for that. Now it's available for all elements.

To expand the size you can use the Get/SetSizeLength() without having to know the exact size.

[mbunkus]

So what's the use of removing such a useful function? Apart from creating more work for me. Yes, I'm a bit salty at the moment due to the amount of churn I have to invest in order to keep MKVToolNix compile with the ever changing libs 2.0 & still keep it compatible with 1.x.

So — honest question. What's gained by removing this function?

[robUx4]

So — honest question. What's gained by removing this function?

Reducing the amount of API we have to support. We should have the bare minimum so that mkvtoolnix and VLC (and mkvalidator/mkclean) work. In this case the start of the data seems more interesting in general than the size of the head. In the end you can deduce one from the other.