doc: Use XREF as anchor prefix in documentation for clearer results in Info viewer. Correctly use @xref, @pxref, @ref macros in documentation. * doc/interpreter/arith.txi, doc/interpreter/basics.txi, doc/interpreter/container.txi, doc/interpreter/debug.txi, doc/interpreter/diagperm.txi, doc/interpreter/eval.txi, doc/interpreter/external.txi, doc/interpreter/func.txi, doc/interpreter/install.txi, doc/interpreter/interp.txi, doc/interpreter/intro.txi, doc/interpreter/java.txi, doc/interpreter/matrix.txi, doc/interpreter/munge-texi.pl, doc/interpreter/numbers.txi, doc/interpreter/package.txi, doc/interpreter/plot.txi, doc/interpreter/sparse.txi, doc/interpreter/stats.txi, doc/interpreter/strings.txi, doc/interpreter/system.txi, doc/interpreter/var.txi, doc/interpreter/vectorize.txi, libinterp/corefcn/error.cc, libinterp/corefcn/qz.cc, libinterp/corefcn/regexp.cc, scripts/general/accumarray.m, scripts/general/structfun.m, scripts/miscellaneous/edit.m, scripts/miscellaneous/setfield.m, scripts/miscellaneous/warning_ids.m, scripts/optimization/fminbnd.m, scripts/optimization/fzero.m, scripts/optimization/lsqnonneg.m: Use XREF as anchor prefix in documentation for clearer results in Info viewer. Correctly use @xref, @pxref, @ref macros in documentation. * scripts/plot/line.m: Remove extra ')' in @deftypefn. * libgui/src/qtinfo/parser.cc(find_ref): Change doc anchor search pattern to XREF.