Fix broken links

Exercises/README.md

@@ -13,18 +13,18 @@ This course requires the use of Python 3.6 or newer.  If you are
 using Python 2, most of the material still applies, but you will
 have to make minor code modifications here and there. 
 
-- link:PythonMastery.pdf[`PythonMastery.pdf`] is a PDF that contains
+- [`PythonMastery.pdf`](../PythonMastery.pdf) is a PDF that contains
 all of the presentation slides.
 
-- The link:Exercises/index.html[`Exercises/`] folder is where you
+- The [`Exercises/`](index.md) folder is where you
 find all the class exercises.
 
-- The `Data/` folder is where you find data files, scripts, and
+- The [`Data/`](../Data/) folder is where you find data files, scripts, and
 other files used by the exercises.
 
-- The `Solutions/` folder contains complete solution code for
+- The [`Solutions/`](../Solutions/) folder contains complete solution code for
 various exercises.  Each problem has its own directory.  For example,
-the solution to exercise 3.2 can be found in the `Solution/3_2/` directory.
+the solution to exercise 3.2 can be found in the [`Solutions/3_2/`](../Solutions/3_2/) directory.
 
 Every attempt has been made to make sure exercises work.  However, it's 
 possible that you will find typos or minor mistakes. If you find any