recover version directory from CMakeLists.txt

this avoid mistakes caused by double declaration of the version
in CMakeLists.txt and conf.py

docs/conf.py

@@ -16,9 +16,18 @@
 # documentation root, use os.path.abspath to make it absolute, like shown here.
 import os
 import sys
+import re
 
 sys.path.insert(0, os.path.abspath('..'))
 
+def get_version():
+    cmake = os.path.join(os.path.dirname(__file__),'../CMakeLists.txt')
+    with open(cmake) as f:
+        for line in f.readlines():
+            m = re.search('set\(VERSION ([\.0-9]+)\)', line)
+            if m:
+                return m.group(1)
+
 # -- General configuration -----------------------------------------------------
 
 # If your documentation needs a minimal Sphinx version, state it here.
@@ -50,7 +59,7 @@ copyright = u'2016, Pierre-Francois Carpentier'
 #
 # The short X.Y version.
 # The full version, including alpha/beta/rc tags.
-release = '0.0.2'
+release = get_version()
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.