adds draw_list to the list library specs (#43)

Author: martin-henz

doc/source_lists.tex

@@ -20,9 +20,13 @@ \subsection*{List Support}
 first element is \lstinline{x1}, the second \lstinline{x2}, etc. Iterative
 process; time: $O(n)$, space: $O(n)$, since the constructed list data structure
 consists of $n$ pairs, each of which takes up a constant amount of space.
+\item \lstinline{draw_list(x)}: Visualizes \lstinline{x} in a separate drawing
+  area in the Source Academy using a box-and-pointer diagram; time, space:
+  $O(n)$, where $n$ is the number of pairs in \lstinline{x}.
 \item \lstinline{equal(x1, x2)}: Returns \lstinline{true} if both
 have the same structure and the same numbers, boolean values, functions or empty list
-at corresponding leaf positions, and \lstinline{false} otherwise.
+at corresponding leaf positions, and \lstinline{false} otherwise; time, space:
+  $O(n)$, where $n$ is the number of pairs in \lstinline{x}.
 \item \lstinline{length(xs)}: Returns the length of the list
   \lstinline{xs}. 
 Iterative process; time: $O(n)$, space: $O(1)$, where $n$ is the length of \lstinline{xs}.