Simplify .py listing code, moving Misc examples.

examples/list_pyfiles.ipy

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+# A simple IPython script that provides Notebook links to .py files in the cwd
+
+from IPython.display import FileLink, display
+files =!ls *.py
+for f in files:
+    display(FileLink(f))

examples/list_subdirs.ipy

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+# A simple IPython script that lists files in all subdirs
+
+from IPython.display import FileLinks, display
+dirs =!ls -d */
+for d in dirs:
+    display(FileLinks(d))