move documentation sources to docs/source

* docs/source/conf.py
  - add toplevel directory to Python search path to allow building of
    documentation using system sphinx installation

docs/source/conf.py

@@ -19,7 +19,8 @@ import sys, os
 # If your extensions are in another directory, add it here. If the directory
 # is relative to the documentation root, use os.path.abspath to make it
 # absolute, like shown here.
-#sys.path.append(os.path.abspath('.'))
+sys.path.append(
+    os.path.abspath(os.path.join(os.path.dirname(__file__), '..', '..')))
 
 # General configuration
 # ---------------------