merge Aj argparse branch into master

argparse material for "Parsing Command Line Arguments" section of the course

_episodes/04-argparse.md

@@ -87,7 +87,6 @@ keypoints:
 > to find another function that could get this for you.
 {: .challenge}
 
-{% include links.md %}
 
 > ##argparse
 
@@ -354,7 +353,7 @@ keypoints:
 {: .challenge}
 
 > ## Options & Arguments Revisited
-> In an earlier exercise (),
+> In an [earlier exercise](#options--arguments),
 > you filled in the blanks in code designed to
 > parse options and arguments from the command line using `sys.argv`.
 > Use what you've learned about `argparse` to write a parser to replace that
@@ -378,4 +377,6 @@ keypoints:
 > Do you think this is better than the approach we used before?
 > If so, do you consider the improvement sufficient to be worth the effort?
 >
-{: .challenge }
\ No newline at end of file
+{: .challenge }
+
+{% include links.md %}
\ No newline at end of file