[API] value, tag lists, caps: add pretty serialization
Submitted by Tim Müller @tpm
Link to original bug (#760027)
Description
Serialized caps or tags can at times be very very long if they contain large buffers, e.g. if streamheaders include coverart.
It would be nice if we had API for 'pretty' serialization of values, tags, caps, structures, etc, so we can use shortened versions in more places including logs and dot files.