Fix ToC.

cca60e3 merged those two sections;  update the references in the table of contents, too.

Author: lehmannro

index.md

@@ -22,8 +22,7 @@ workshop then that will be perfect.
 * [Recap of Python essentials](core/recap.html) - A quick recap of some of the Introduction to Programming essentials.
 * [Data Structures in Python](core/data.html) - An introduction to the list and dictionary data structures.
 * [Introducing IPython Notebook](core/notebook.html) - A whole new way to work with Python!
-* [Working With Text Files](core/text-files.html) - What is a text file? How do we get them in and out of Python?
-* [Working With Strings](core/strings.html) - Once we have our text in Python, what can we do with it?
+* [Analyzing a survey](core/survey.html) - Once we have our text in Python, what can we do with it?
 * [Creating Charts](core/charts.html) - Using IPython Notebook with matplotlib to create charts.
 * [CSV Files](core/csv.html) - Reading comma-separated data.