ox.el: add smart quotes for greek

* lisp/ox.el (org-export-smart-quotes-alist): The correct quotes for
Greek have been established with the help of Protesilaos Stavrou, who
has contributed a style guide for the European institutions:
http://publications.europa.eu/code/el/el-4100107el.htmq On the correct
character for Greek second-level opening quotes, according to Yannis
Haralambous (`From Unicode to Typography, a Case Study: the Greek
Script' (1999, p. 20), a symbol equivalent to the Unicode character
U+201F is historically attested. But it seems that the current trend
in Greece is to apply the character U+201C, more commonly used in
other languages. Haralambous himself, in a recent consultation,
states: `[...] U+201C is a good choice for representing that grapheme
since it is used in most countries of the world...'

lisp/ox.el

@@ -5437,6 +5437,16 @@ transcoding it."
      (secondary-closing
       :utf-8 "‘" :html "‘" :latex "\\grq{}" :texinfo "@quoteleft{}")
      (apostrophe :utf-8 "’" :html "’"))
+    ("el"
+     (primary-opening
+      :utf-8 "«" :html "«" :latex "\\guillemotleft{}"
+      :texinfo "@guillemetleft{}")
+     (primary-closing
+      :utf-8 "»" :html "»" :latex "\\guillemotright{}"
+      :texinfo "@guillemetright{}")
+     (secondary-opening :utf-8 "“" :html "“" :latex "``" :texinfo "``")
+     (secondary-closing :utf-8 "”" :html "”" :latex "''" :texinfo "''")
+     (apostrophe :utf-8 "’" :html "’"))
     ("en"
      (primary-opening :utf-8 "“" :html "“" :latex "``" :texinfo "``")
      (primary-closing :utf-8 "”" :html "”" :latex "''" :texinfo "''")