config,proxy: add new configuration logToStdout (#432)

The new logToStdout option controls what is logged to stdout. The
default has been changed to just the proxy logs, which contain swap and
http request logs.

There are four supported settings: none, proxy, upstream, both. The
"both" setting is the legacy setting where everything was spewed to
stdout.

proxy/config/config_windows_test.go

@@ -158,6 +158,7 @@ groups:
 	expected := Config{
 		LogLevel:      "info",
 		LogTimeFormat: "",
+		LogToStdout:   LogToStdoutProxy,
 		StartPort:     5800,
 		Macros: MacroList{
 			{"svr-path", "path/to/server"},