doc: attempt to parse version if not in environment

Should fix the version displayed on readthedocs.

doc/userguide/conf.py

@@ -15,6 +15,7 @@
 import sys
 import os
 import shlex
+import re
 
 on_rtd = os.environ.get('READTHEDOCS', None) == 'True'
 
@@ -57,8 +58,18 @@ author = u'OISF'
 # built documents.
 #
 # The short X.Y version.
-version = os.environ.get('version', "unknown")
-# The full version, including alpha/beta/rc tags.
+
+# Attempt to extract the version configure.ac.
+try:
+    version = os.environ.get('version', None)
+    if not version:
+        version = re.search(
+            "AC_INIT\(suricata,\s*(.*)?\)",
+            open("../../configure.ac").read()).groups()[0]
+    if not version:
+        version = "unknown"
+except:
+    version = "unknown"
 release = version
 
 # The language for content autogenerated by Sphinx. Refer to documentation