Use XDG data directory for user data directory.

Instead of `$HOME/.pandoc`, the default user data directory is
now `$XDG_DATA_HOME/pandoc`, where `XDG_DATA_HOME` defaults to
`$HOME/.local/share` but can be overridden by setting the environment
variable.

If this directory is missing, then `$HOME/.pandoc` is searched
instead, for backwards compatibility.  However, we recommend
moving local pandoc data files from `$HOME/.pandoc` to
`$HOME/.local/share/pandoc`.

On Windows the default user data directory remains the same.

Closes #3582.

1 files changed, 7 insertions, 12 deletions

diff --git a/MANUAL.txt b/MANUAL.txt
index 8ef6c54e3..50ca91300 100644
--- a/MANUAL.txt
+++ b/MANUAL.txt
@@ -349,18 +349,13 @@ General options {.options}
 
 :   Specify the user data directory to search for pandoc data files.
     If this option is not specified, the default user data directory
-    will be used.  This is, in UNIX:
-
-        $HOME/.pandoc
-
-    in Windows XP:
-
-        C:\Documents And Settings\USERNAME\Application Data\pandoc
-
-    and in Windows Vista or later:
-
-        C:\Users\USERNAME\AppData\Roaming\pandoc
-
+    will be used.  On \*nix and macOS systems this will be the `pandoc`
+    subdirectory of the XDG data directory (by default,
+    `$HOME/.local/share`, overridable by setting the `XDG_DATA_HOME`
+    environment variable).  If that directory does not exist,
+    `$HOME/.pandoc` will be used (for backwards compatibility).
+    In Windows the default user data directory is
+    `C:\Users\USERNAME\AppData\Roaming\pandoc`.
     You can find the default user data directory on your system by
     looking at the output of `pandoc --version`.
     A `reference.odt`, `reference.docx`, `epub.css`, `templates`,