Fix shell completion issues and documentation

This issue was raised in #990. The completer was never used in Python3.4+,
because it was overwritten by Python's completer. Oddly enough it has always
worked in Python2.7/3.3.

The documentation was also slightly modified. os.path.join was always a
complex beast.

jedi/utils.py

@@ -108,6 +108,11 @@ def setup_readline(namespace_module=__main__):
                 return None
 
     try:
+        # Need to import this one as well to make sure it's executed before
+        # this code. This didn't use to be an issue until 3.3. Starting with
+        # 3.4 this is different, it always overwrites the completer if it's not
+        # already imported here.
+        import rlcompleter
         import readline
     except ImportError:
         print("Jedi: Module readline not available.")