Remove lumberjack logger (#257)

* Removed lumberjack from coremain

As is mentioned in 251, this fix removed lumberjack from coremain.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Remove lumberjack from log middleware

As mentioned in 251, lumberjack is not suitable for applications like CoreDNS
so it is removed from the log middleware.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Update log/README.md as lumberjack has been removed

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Adjust default log output from `ioutil.Discard` to `os.Stdout`

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

middleware/pkg/roller/roller.go

@@ -1,62 +0,0 @@
-package roller
-
-import (
-	"io"
-	"strconv"
-
-	"github.com/mholt/caddy"
-	"gopkg.in/natefinch/lumberjack.v2"
-)
-
-func Parse(c *caddy.Controller) (*LogRoller, error) {
-	var size, age, keep int
-	// This is kind of a hack to support nested blocks:
-	// As we are already in a block: either log or errors,
-	// c.nesting > 0 but, as soon as c meets a }, it thinks
-	// the block is over and return false for c.NextBlock.
-	for c.NextBlock() {
-		what := c.Val()
-		if !c.NextArg() {
-			return nil, c.ArgErr()
-		}
-		value := c.Val()
-		var err error
-		switch what {
-		case "size":
-			size, err = strconv.Atoi(value)
-		case "age":
-			age, err = strconv.Atoi(value)
-		case "keep":
-			keep, err = strconv.Atoi(value)
-		}
-		if err != nil {
-			return nil, err
-		}
-	}
-	return &LogRoller{
-		MaxSize:    size,
-		MaxAge:     age,
-		MaxBackups: keep,
-		LocalTime:  true,
-	}, nil
-}
-
-// LogRoller implements a middleware that provides a rolling logger.
-type LogRoller struct {
-	Filename   string
-	MaxSize    int
-	MaxAge     int
-	MaxBackups int
-	LocalTime  bool
-}
-
-// GetLogWriter returns an io.Writer that writes to a rolling logger.
-func (l LogRoller) GetLogWriter() io.Writer {
-	return &lumberjack.Logger{
-		Filename:   l.Filename,
-		MaxSize:    l.MaxSize,
-		MaxAge:     l.MaxAge,
-		MaxBackups: l.MaxBackups,
-		LocalTime:  l.LocalTime,
-	}
-}