doc: use colors for diagnostics in TeX too

Thanks to Gavin Smith and Patrice Dumas.
http://lists.gnu.org/archive/html/help-texinfo/2019-04/msg00015.html

* doc/bison.texi (@colorWarning, @colorError, @colorNotice)
(@colorOff): Define for TeX and HTML.
(@dwarning, @derror, @dnotice): Use them.

THANKS

@@ -66,6 +66,7 @@ Frank Heckenbach          frank@g-n-u.de
 Frans Englich             frans.englich@telia.com
 Gabriel Rassoul           gabriel.rassoul@epita.fr
 Gary L Peskin             garyp@firstech.com
+Gavin Smith               gavinsmith0123@gmail.com
 Georg Sauthoff            gsauthof@TechFak.Uni-Bielefeld.DE
 George Neuner             gneuner2@comcast.net
 Gilles Espinasse          g.esp@free.fr
@@ -128,6 +129,7 @@ Oliver Mangold            o.mangold@gmail.com
 Paolo Bonzini             bonzini@gnu.org
 Paolo Simone Gasparello   djgaspa@gmail.com
 Pascal Bart               pascal.bart@epita.fr
+Patrice Dumas             pertusus@free.fr
 Paul Eggert               eggert@cs.ucla.edu
 Paul Hilfinger            Hilfinger@CS.Berkeley.EDU
 Per Allansson             per@appgate.com