Fix spacing markup and other sundries.

Doc/ext/extending.tex

-\chapter{Extending Python with C or \Cpp \label{intro}}
+\chapter{Extending Python with \C{} or \Cpp{} \label{intro}}
 
 
 It is quite easy to add new built-in modules to Python, if you know
@@ -349,7 +349,7 @@ initspam(void)
 
 Note that PyMODINIT_FUNC declares the function as \code{void} return type, 
 declares any special linkage declarations required by the platform, and for 
-\Cpp declares the function as \code{extern "C"}.
+\Cpp{} declares the function as \code{extern "C"}.
 
 When the Python program imports module \module{spam} for the first
 time, \cfunction{initspam()} is called. (See below for comments about