Add SetLogger to *Conn

Allow replacing logger after connection is established. Also
refactor internals of logging such that there is a log method that
adds the pid to all log calls instead of making a new logger object.
The reason for this is so pid will be logged regardless of whether
loggers are replaced and restored.

logger.go

@@ -30,31 +30,6 @@ type Logger interface {
 	Error(msg string, ctx ...interface{})
 }
 
-type connLogger struct {
-	logger Logger
-	pid    int32
-}
-
-func (l *connLogger) Debug(msg string, ctx ...interface{}) {
-	ctx = append(ctx, "pid", l.pid)
-	l.logger.Debug(msg, ctx...)
-}
-
-func (l *connLogger) Info(msg string, ctx ...interface{}) {
-	ctx = append(ctx, "pid", l.pid)
-	l.logger.Info(msg, ctx...)
-}
-
-func (l *connLogger) Warn(msg string, ctx ...interface{}) {
-	ctx = append(ctx, "pid", l.pid)
-	l.logger.Warn(msg, ctx...)
-}
-
-func (l *connLogger) Error(msg string, ctx ...interface{}) {
-	ctx = append(ctx, "pid", l.pid)
-	l.logger.Error(msg, ctx...)
-}
-
 // Converts log level string to constant
 //
 // Valid levels: