Add Metaparse to the list of libraries documented using BoostBook

doc/src/boost.xml

@@ -56,6 +56,7 @@
    <xi:include href="../../libs/lambda/doc/lambda.xml"/>
    <xi:include href="lexical_cast.xml"/>
    <xi:include href="lockfree.xml"/>
+   <xi:include href="metaparse.xml"/>
    <xi:include href="move.xml"/>
    <xi:include href="../../libs/multi_array/doc/xml/bbref.xml"/>
    <xi:include href="mpi.xml"/>