Switch to data.xml for SVG transformation to fix label offset in plots

This change switches to data.xml for SVG transformation.

data.xml preserves the whitespace from the source document, so this should fix #17.

• I am depending on data.xml 0.2.0-alpha5 because only the 0.2.0 series includes XML namespace support, which is needed for SVG. As far as I know, the alpha is quite stable.
• I made one change to preserve metadata during the ID mangling. data.xml needs this metadata to generate the right XML namespace prefixes during emitting.

The worksheets I tried (and examined) with different plots etc. all look good, so this seems to completely resolve the issue!

Hello @sbelak,

I think this change (or a similar one) would be quite valuable, because it fixes a visual bug that’s noticeable in all Huri plots today. The plots are a bit awkward to use in presentations for example, because all the labels are slightly off.

I would be very happy if you could consider including it.

Thank you, David