Added request logger middleware which helps to use custom logger library for logging requests

[aldas]

Added request logger middleware which helps to use custom logger library for logging requests.

Usage would be as follows:

---

Example for fmt.Printf

    e.Use(middleware.RequestLoggerWithConfig(middleware.RequestLoggerConfig{
        LogStatus: true,
        LogURI:    true,
        LogValuesFunc: func(c echo.Context, v middleware.RequestLoggerValues) error {
            fmt.Printf("REQUEST: uri: %v, status: %v\n", v.URI, v.Status)
            return nil
        },
    }))

Example for Zerolog (https://github.com/rs/zerolog)

    logger := zerolog.New(os.Stdout)
    e.Use(middleware.RequestLoggerWithConfig(middleware.RequestLoggerConfig{
        LogURI:    true,
        LogStatus: true,
        LogValuesFunc: func(c echo.Context, v middleware.RequestLoggerValues) error {
            logger.Info().
                Str("URI", v.URI).
                Int("status", v.Status).
                Msg("request")

            return nil
        },
    }))

Example for Zap (https://github.com/uber-go/zap)

    logger, _ := zap.NewProduction()
    e.Use(middleware.RequestLoggerWithConfig(middleware.RequestLoggerConfig{
        LogURI:    true,
        LogStatus: true,
        LogValuesFunc: func(c echo.Context, v middleware.RequestLoggerValues) error {
            logger.Info("request",
                zap.String("URI", v.URI),
                zap.Int("status", v.Status),
            )

            return nil
        },
    }))

Example for Logrus (https://github.com/sirupsen/logrus)

    log := logrus.New()
    e.Use(middleware.RequestLoggerWithConfig(middleware.RequestLoggerConfig{
        LogURI:    true,
        LogStatus: true,
        LogValuesFunc: func(c echo.Context, values middleware.RequestLoggerValues) error {
            log.WithFields(logrus.Fields{
                "URI":    values.URI,
                "status": values.Status,
            }).Info("request")

            return nil
        },
    }))

---

Note about benchmarks for RequestLogger - these do not format message and therefore are not 1-to-1 comparable with Logger middleware performance.

// without header/query/form fields
BenchmarkLoggerWithConfig_withoutMapFields-6         428011          2713 ns/op        1472 B/op         24 allocs/op
BenchmarkRequestLogger_withoutMapFields-6            721497          1567 ns/op        1384 B/op         17 allocs/op

// with header/query/form fields
BenchmarkLoggerWithConfig_withMapFields-6            330147          3585 ns/op        1937 B/op         29 allocs/op
BenchmarkRequestLogger_withMapFields-6               429079          3113 ns/op        3048 B/op         28 allocs/op

[codecov]

Codecov Report

Merging #1980 (536f5e7) into master (7f502b1) will increase coverage by 0.18%.
The diff coverage is 97.56%.

@@            Coverage Diff             @@
##           master    #1980      +/-   ##
==========================================
+ Coverage   91.04%   91.22%   +0.18%     
==========================================
  Files          32       33       +1     
  Lines        2802     2884      +82     
==========================================
+ Hits         2551     2631      +80     
- Misses        160      161       +1     
- Partials       91       92       +1     

Impacted Files	Coverage Δ
echo.go	94.15% <ø> (ø)
middleware/request_logger.go	97.56% <97.56%> (ø)

---

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[aldas]

@pafuent , @lammel or @vishr any of you please review this PR.

[pafuent]

LGTM!!!
I added some comments about minors things.
Thanks @aldas for being so active on Echo community!!!