huge refactoring

internal/pkg/xlog/doc.go

@@ -0,0 +1,17 @@
+/*
+Package xlog defines a standard logger
+for the application.
+
+It uses structured logging thanks to
+https://github.com/sirupsen/logrus.
+
+All messages have at least two fields:
+
+A "trace" field which helps to identify
+messages belonging to the same context.
+
+An "op" field which helps to identify
+the logical operation associated
+with the message.
+*/
+package xlog