Added support for configuring traces

As discussed by email a couple of months ago, this has minor changes to support configuration of traces.  Sample configuration is:

[
 {lager, 
  [
   {crash_log, "log/crash.log"},
   {crash_log_size, 65536},
   {error_logger_redirect, true},
   {handlers, 
    [
     {lager_console_backend, none},
     {lager_file_backend, [
                           {"log/error.log", error, 10485760, "$D0", 5},
                           {"log/console.log", none, 10485760, "$D0", 5},
                           {"log/sip_protocol.log", none, 10485760, "$D0", 5}
                          ]}
    ]},
   {traces, 
    [
     {lager_console_backend, [{type, normal}], debug},
     {{lager_file_backend, "log/console.log"}, [{type, normal}], debug},
     {{lager_file_backend, "log/sip_protocol.log"}, [{type, sip_protocol}], debug}
    ]}
  ]}
].