Add more appropriate markup.

doc/src/sgml/array.sgml

doc/src/sgml/charset.sgml

doc/src/sgml/client-auth.sgml

doc/src/sgml/datatype.sgml

doc/src/sgml/ddl.sgml

doc/src/sgml/developer.sgml

doc/src/sgml/dfunc.sgml

doc/src/sgml/diskusage.sgml

doc/src/sgml/ecpg.sgml

doc/src/sgml/extend.sgml

doc/src/sgml/features.sgml

doc/src/sgml/func.sgml

doc/src/sgml/indices.sgml

doc/src/sgml/installation.sgml

doc/src/sgml/jdbc.sgml

doc/src/sgml/libpgtcl.sgml

doc/src/sgml/libpq.sgml

doc/src/sgml/maintenance.sgml

doc/src/sgml/monitoring.sgml

doc/src/sgml/mvcc.sgml