It's just synctactic sugar, but it is always better than executing string
concatenations in one's mind.
Do not do this with files in src/static, because we want to keep IE 11
compatibility.
If you edit `src/templates/export_html.html` to remove the
`<meta name="changedby" content="Etherpad">` tag[1], PDF export with
soffice has a bug: the first word of the pad is deleted and a blank page
is inserted as first page (the pad's text begins on the second page).
The `--writer` soffice option avoids that bug.
[1] you may want to delete that tag since it is inserted as a comment in
.doc or .odt soffice export.
When using LibreOffice to convert pads to doc, we got `Error: no export filter for /tmp/xxxx.doc` (tested with LO 5 and 6). Maybe it's a regression from LO. Anyway, converting HTML to odt, then to doc works.
Thx to lpagliari for her review!