dtd: Add several new elements
This allows us to validate the libhandy dtd again:
https://source.puri.sm/Librem5/libhandy/merge_requests/135/diffs
Edited by Guido Günther
This allows us to validate the libhandy dtd again:
https://source.puri.sm/Librem5/libhandy/merge_requests/135/diffs