feat: Add a new ErrorHandlerWithContext (#1328)
feat: Add a new ErrorHandlerWithContext (#1328)

* feat: Add a new ErrorHandlerWithContext

This commit adds a new error handler, which is passed the 
current context, so that you can add custom redirects or even
other kinds of responses. For example:

```go
	e.Use(middleware.JWTWithConfig(middleware.JWTConfig{
		SigningKey: []byte("secret"),
		TokenLookup: "query:token",
		ErrorHandlerWithContext: func(err error, c echo.Context) error {
			// do stuff with context and err
			switch err.(type) {
			case jwt.ValidationError:
				return c.Redirect(http.StatusSeeOther, "/login")
			}
			return err
		},
	}))
```

* chore: address golint issues

labstack/echo,labstack/echo