[new.delete.single], [smartptr.util.getdeleter] Replace literal 0 with nullptr.

Fixes #243 and #244

Author: jwakely

source/support.tex

@@ -1654,7 +1654,7 @@
 \enterexample
 \begin{codeblock}
 T* p1 = new T;                  // throws \tcode{bad_alloc} if it fails
-T* p2 = new(nothrow) T;         // returns \tcode{0} if it fails
+T* p2 = new(nothrow) T;         // returns \tcode{nullptr} if it fails
 \end{codeblock}
 \exitexample
 \end{itemdescr}

source/utilities.tex

@@ -6273,7 +6273,7 @@
 
 \begin{itemdescr}
 \pnum\returns  If \tcode{p} \textit{owns} a deleter \tcode{d} of type cv-unqualified
-\tcode{D}, returns \tcode{\&d}; otherwise returns \tcode{0}. The returned
+\tcode{D}, returns \tcode{\&d}; otherwise returns \tcode{nullptr}. The returned
 pointer remains valid as long as there exists a \tcode{shared_ptr} instance
 that owns \tcode{d}. \enternote It is unspecified whether the pointer
 remains valid longer than that. This can happen if the implementation doesn't destroy