org-entities.el (org-entities): Add Amacr and amacr entities

Thanks to Karel Sprenger for the suggestion.

lisp/org-entities.el

@@ -88,6 +88,8 @@ packages to be loaded, add these packages to `org-latex-packages-alist'."
      ("aacute" "\\'{a}" nil "á" "a" "á" "á")
      ("Acirc" "\\^{A}" nil "Â" "A" "Â" "Â")
      ("acirc" "\\^{a}" nil "â" "a" "â" "â")
+     ("Amacr" "\\bar{A}" nil "Ā" "A" "Ã" "Ã")
+     ("amacr" "\\bar{a}" nil "ā" "a" "ã" "ã")
      ("Atilde" "\\~{A}" nil "Ã" "A" "Ã" "Ã")
      ("atilde" "\\~{a}" nil "ã" "a" "ã" "ã")
      ("Auml" "\\\"{A}" nil "Ä" "Ae" "Ä" "Ä")