Do not use errgo nor pkg/errors for root errors

Related to #582

errors/errctx.go

@@ -2,6 +2,8 @@ package errors
 
 import (
 	"context"
+	stderrors "errors"
+	"fmt"
 
 	"github.com/pkg/errors"
 	"gopkg.in/errgo.v1"
@@ -25,30 +27,41 @@ func (err ErrCtx) Unwrap() error {
 	return err.err
 }
 
-func New(ctx context.Context, message string) error {
-	return ErrCtx{ctx: ctx, err: errgo.New(message)}
+// New wraps errors.New from the standard library
+//
+// These errors are usually created outside any function code at the top of
+// files, so no context is needed nor wrapping is needed.
+func New(message string) error {
+	return stderrors.New(message)
+}
+
+func NewWithCtx(ctx context.Context, message string) error {
+	return ErrCtx{ctx: ctx, err: errors.New(message)}
 }
 
 func Newf(ctx context.Context, format string, args ...interface{}) error {
-	return ErrCtx{ctx: ctx, err: errgo.Newf(format, args...)}
+	return ErrCtx{ctx: ctx, err: fmt.Errorf(format, args...)}
+}
+
+func Errorf(ctx context.Context, format string, args ...interface{}) error {
+	return Newf(ctx, format, args...)
 }
 
+// Notef is wrapping an error with the underneath errgo library
 func Notef(ctx context.Context, err error, format string, args ...interface{}) error {
 	return ErrCtx{ctx: ctx, err: errgo.Notef(err, format, args...)}
 }
 
+// Wrap is wrapping an error with the underneath errgo library
 func Wrap(ctx context.Context, err error, message string) error {
 	return ErrCtx{ctx: ctx, err: errors.Wrap(err, message)}
 }
 
+// Wrapf is wrapping an error with the underneath errgo library
 func Wrapf(ctx context.Context, err error, format string, args ...interface{}) error {
 	return ErrCtx{ctx: ctx, err: errors.Wrapf(err, format, args...)}
 }
 
-func Errorf(ctx context.Context, format string, args ...interface{}) error {
-	return ErrCtx{ctx: ctx, err: errors.Errorf(format, args...)}
-}
-
 // RootCtxOrFallback unwrap all wrapped errors from err to get the deepest context
 // from ErrCtx errors. If there is no wrapped ErrCtx RootCtxOrFallback returns ctx from parameter.
 func RootCtxOrFallback(ctx context.Context, err error) context.Context {