🎨 Introduce contextualized logging

This commit is multi-fold as it also refactors internally context and logger
as interfaces so it is easier to plug luet as a library externally.

Introduces a garbage collector (related to #227) but doesn't handle yet
parallelism.

Closes #265

vendor/github.com/ipfs/go-log/v2/log.go

@@ -0,0 +1,84 @@
+// Package log is the logging library used by IPFS & libp2p
+// (https://github.com/ipfs/go-ipfs).
+package log
+
+import (
+	"time"
+
+	"go.uber.org/zap"
+	"go.uber.org/zap/zapcore"
+)
+
+// StandardLogger provides API compatibility with standard printf loggers
+// eg. go-logging
+type StandardLogger interface {
+	Debug(args ...interface{})
+	Debugf(format string, args ...interface{})
+	Error(args ...interface{})
+	Errorf(format string, args ...interface{})
+	Fatal(args ...interface{})
+	Fatalf(format string, args ...interface{})
+	Info(args ...interface{})
+	Infof(format string, args ...interface{})
+	Panic(args ...interface{})
+	Panicf(format string, args ...interface{})
+	Warn(args ...interface{})
+	Warnf(format string, args ...interface{})
+}
+
+// EventLogger extends the StandardLogger interface to allow for log items
+// containing structured metadata
+type EventLogger interface {
+	StandardLogger
+}
+
+// Logger retrieves an event logger by name
+func Logger(system string) *ZapEventLogger {
+	if len(system) == 0 {
+		setuplog := getLogger("setup-logger")
+		setuplog.Error("Missing name parameter")
+		system = "undefined"
+	}
+
+	logger := getLogger(system)
+	skipLogger := logger.Desugar().WithOptions(zap.AddCallerSkip(1)).Sugar()
+
+	return &ZapEventLogger{
+		system:        system,
+		SugaredLogger: *logger,
+		skipLogger:    *skipLogger,
+	}
+}
+
+// ZapEventLogger implements the EventLogger and wraps a go-logging Logger
+type ZapEventLogger struct {
+	zap.SugaredLogger
+	// used to fix the caller location when calling Warning and Warningf.
+	skipLogger zap.SugaredLogger
+	system     string
+}
+
+// Warning is for compatibility
+// Deprecated: use Warn(args ...interface{}) instead
+func (logger *ZapEventLogger) Warning(args ...interface{}) {
+	logger.skipLogger.Warn(args...)
+}
+
+// Warningf is for compatibility
+// Deprecated: use Warnf(format string, args ...interface{}) instead
+func (logger *ZapEventLogger) Warningf(format string, args ...interface{}) {
+	logger.skipLogger.Warnf(format, args...)
+}
+
+// FormatRFC3339 returns the given time in UTC with RFC3999Nano format.
+func FormatRFC3339(t time.Time) string {
+	return t.UTC().Format(time.RFC3339Nano)
+}
+
+func WithStacktrace(l *ZapEventLogger, level LogLevel) *ZapEventLogger {
+	copyLogger := *l
+	copyLogger.SugaredLogger = *copyLogger.SugaredLogger.Desugar().
+		WithOptions(zap.AddStacktrace(zapcore.Level(level))).Sugar()
+	copyLogger.skipLogger = *copyLogger.SugaredLogger.Desugar().WithOptions(zap.AddCallerSkip(1)).Sugar()
+	return &copyLogger
+}