Update maintainer list.

libs/maintainers.txt

@@ -23,6 +23,7 @@ atomic                Helge Bahmann <hcb -at- chaoticmind.net>, Tim Blechmann <t
 beast                 Vinnie Falco <vinnie.falco@gmail.com>
 bimap                 Matias Capeletto <matias.capeletto -at- gmail.com>
 bind                  Peter Dimov <pdimov -at- pdimov.com>
+callable_traits       Barrett Adair <barrettellisadair -at- gmail.com>
 chrono                Vicente J. Botet Escriba <vicente.botet -at- wanadoo.fr>
 chrono/stopwatch      Vicente J. Botet Escriba <vicente.botet -at- wanadoo.fr>
 circular_buffer       Jan Gaspar <jano_gaspar -at- yahoo.com>