Copy-free access to Exiv2::DataValue

[jim-easterbrook]

An Exiv2::DataValue value could be a large block of binary data. Other data blocks, such as Exiv2::PreviewImage, have methods like pData() to allow copy-free reading of their data. Is there some good reason that I haven't spotted why DataValue doesn't?

[neheb]

PR welcome I guess.

[jim-easterbrook]

An easy way to provide this would be to make DataValue::value_ public, as is the case for many other Value subclasses. Then one could use any std::vector methods on the data.