NB CH-6 (C++14 CD) [over.literal]: Mark reserved example as such.

Mark the existing example for user-defined literals with the plain
"E" suffix as reserved for clarity.

Closes #181.

Author: sdutoit

source/overloading.tex

@@ -3219,7 +3219,7 @@
 void operator "" _km(long double);                  // OK
 string operator "" _i18n(const char*, std::size_t); // OK
 template <char...> double operator "" _\u03C0();    // OK: UCN for lowercase pi
-float operator ""E(const char*);                    // OK
+float operator ""E(const char*);                    // OK, but reserved~(\ref{usrlit.suffix})
 float operator " " B(const char*);                  // error: non-empty \grammarterm{string-literal}
 string operator "" 5X(const char*, std::size_t);    // error: invalid literal suffix identifier
 double operator "" _miles(double);                  // error: invalid \grammarterm{parameter-declaration-clause}