[diff.cpp03.library] Correct \effect to \change

- Correct \effect to \change.
- Add period at end.
- Add \tcode for swap.

source/compatibility.tex

@@ -2340,12 +2340,12 @@
 invalid in this revision of \Cpp{}.
 
 \diffref{swappable.requirements}
-\effect
-Function \tcode{swap} moved to a different header
+\change
+Function \tcode{swap} moved to a different header.
 \rationale
 Remove dependency on \libheaderref{algorithm} for \tcode{swap}.
 \effect
-Valid \CppIII{} code that has been compiled expecting swap to be in
+Valid \CppIII{} code that has been compiled expecting \tcode{swap} to be in
 \libheaderref{algorithm} may have to instead include \libheaderref{utility}.
 
 \diffref{namespace.posix}