Support For XPF Format Version 2.0

[gangsterofboats]

Earlier this year Jim Horne updated the XPF format from version 1.0 to the current version 2.0, in part to be similar to the output of his Across Lite To Text program. Among the other changes he made is some of the XML tags are renamed, thus the XPFv2.0 files cannot be read by XWord, hence this issue.

[jpd236]

Adding support for reading the new version shouldn't be too difficult. One question here is what we should do when saving - do we just save using the new version too, or is there value in maintaining backwards compatibility by saving in the old format? Some options could be:

1. Support XPF 2.0 as a fully separate format (so user has to choose to save in 1.0 or 2.0)
2. Drop write support for XPF 1.0; always write as 2.0.
3. Write as 2.0 except when the original input was XPF 1.0, in which case we use that version.