[multibyte.strings] Move punctuation out of \term. (#1437)

Author: Eelis

source/lib-intro.tex

@@ -829,13 +829,10 @@
 \rSec5[multibyte.strings]{Multibyte strings}
 
 \pnum
-A
 \indextext{NTBS}%
 \indextext{NTMBS}%
-\term{null-terminated multibyte string,}
-or \ntmbs,
-\indextext{string!null-terminated multibyte}%
-is an \ntbs that constitutes a
+A \defnx{null-terminated multibyte string}{string!null-terminated multibyte},
+or \ntmbs, is an \ntbs that constitutes a
 sequence of valid multibyte characters, beginning and ending in the initial
 shift state.\footnote{An \ntbs that contains characters only from the
 basic execution character set is also an \ntmbs.