Update httlacs to modern project

Also fix links to labs.

Author: bnmnetp

pretext/Dictionaries/Sparsematrices.ptx

@@ -50,7 +50,7 @@ print(matrix.get((1, 3), 0))
     <p>
       <ul>
         <li>
-          <p><url href="../Labs/lab12_01.html" visual="../Labs/lab12_01.html">Counting Letters</url> In this guided lab exercise we will work
+          <p>Counting Letters <xref ref="labs_counting-letters" /> In this guided lab exercise we will work
                         through a problem solving exercise that will use dictionaries to generalize the solution
                         to counting the occurrences of all letters in a string.</p>
         </li>
@@ -62,7 +62,7 @@ print(matrix.get((1, 3), 0))
     <p>
       <ul>
         <li>
-          <p><url href="../Labs/lab12_02.html" visual="../Labs/lab12_02.html">Letter Count Histogram</url> Combine the previous lab with the histogram example.</p>
+          <p>Letter Count Histogram <xref ref="labs_letter-count-histogram" /> Combine the previous lab with the histogram example.</p>
         </li>
       </ul>
     </p>