fix to the code to make it behave like the module docstring.
An interpreter instance will recognize a command name \samp{foo} if
and only if it has a method \method{do_foo()}. As a special case,
-a line containing only the character \character{?} is dispatched to
+a line beginning with the character \character{?} is dispatched to
the method \method{do_help()}. As another special case, a line
-containing only the character \character{!} is dispatched to the
+beginning with the character \character{!} is dispatched to the
method \method{do_shell} (if such a method is defined).
All subclasses of \class{Cmd} inherit a predefined \method{do_help}.