create xdg user dirs

Users who think the default directories are stupid will want to create a
~/.config/user-dirs.dirs file to specify alternatives, or to disable
certain directories. Disable directories by pointing them toward your
home dir: https://freedesktop.org/wiki/Software/xdg-user-dirs/#settings

Example:
7182e0d787

closes #45

roles/x/tasks/main.yml

@@ -30,3 +30,4 @@
 - include: srandrd.yml
 - include: termite.yml
 - include: autocutsel.yml
+- include: xdg.yml

roles/x/tasks/xdg.yml

@@ -0,0 +1,12 @@
+---
+- name: Install xdg-user-dirs
+  pacman: name=xdg-user-dirs state=present
+  tags:
+    - xdg
+
+- name: Create user directories
+  command: /usr/bin/xdg-user-dirs-update
+  become: yes
+  become_user: "{{ user.name }}"
+  tags:
+    - xdg