add exception class hierarchy. This should probably be done differently,
but at least the content is there.
diff --git a/Doc/lib/libexcs.tex b/Doc/lib/libexcs.tex
index f4b1d15..c865eea 100644
--- a/Doc/lib/libexcs.tex
+++ b/Doc/lib/libexcs.tex
@@ -383,3 +383,47 @@
\begin{excdesc}{RuntimeWarning}
Base class for warnings about dubious runtime behavior.
\end{excdesc}
+
+The full Exception class hierarchy is:
+
+\begin{verbatim}
+ Exception
+ +-- SystemExit
+ +-- StopIteration
+ +-- StandardError
+ | +-- KeyboardInterrupt
+ | +-- ImportError
+ | +-- EnvironmentError
+ | | +-- IOError
+ | | +-- OSError
+ | | +-- WindowsError
+ | +-- EOFError
+ | +-- RuntimeError
+ | | +-- NotImplementedError
+ | +-- NameError
+ | | +-- UnboundLocalError
+ | +-- AttributeError
+ | +-- SyntaxError
+ | | +-- IndentationError
+ | | +-- TabError
+ | +-- TypeError
+ | +-- AssertionError
+ | +-- LookupError
+ | | +-- IndexError
+ | | +-- KeyError
+ | +-- ArithmeticError
+ | | +-- OverflowError
+ | | +-- ZeroDivisionError
+ | | +-- FloatingPointError
+ | +-- ValueError
+ | | +-- UnicodeError
+ | +-- ReferenceError
+ | +-- SystemError
+ | +-- MemoryError
+ +---Warning
+ +-- UserWarning
+ +-- DeprecationWarning
+ +-- SyntaxWarning
+ +-- OverflowWarning
+ +-- RuntimeWarning
+\end{verbatim}