Changes:

• preview server (stog-server), using xmldiff.js package and websockets,
• use Xtmpl 0.10 to unescape entities in attributes of final documents,
• new plugin ,
• new rules print-date and print-datetime,
• keep /index.html in urls when the site url scheme is "file:",
• handle subtitle in article default template,
• improve latex translator,
• allow use-parent-path="false" in , not to use parent path when forging new elements' path,
• improve provided templates and math module,
• various fixes,
• replace calls to OCaml deprecated functions,
• use safe-string (require OCaml >= 4.02).