* Remove output parameter from NewLogger function

* Implement SetOutput method
* Write log method's errors to internal error output
* Implement SetInternalErrorOutput method
* Improve synchronization
* Remove unnecessary methods
* Initialize go modules
* Update readme
* Format code
* Update tests

.gitignore

@@ -12,7 +12,4 @@
 *.out
 
 # Dependency directories (remove the comment below to include it)
-# vendor/
-
-# GoLand
-.idea/
+# vendor/

README.md

@@ -1,35 +1,41 @@
 # log
+
 Simple, customizable, leveled and efficient logging in Go
 
 [![Go](https://github.com/ermanimer/log/actions/workflows/go.yml/badge.svg?branch=main)](https://github.com/ermanimer/log/actions/workflows/go.yml) [![Go Report Card](https://goreportcard.com/badge/github.com/ermanimer/log)](https://goreportcard.com/report/github.com/ermanimer/log)
 
 # Installation
+
 ```bash
 go get -u github.com/ermanimer/log
 ```
 
 # Features
+
 **log** is a simple logging package for Go. 
 
-- You can set time format and prefixes. 
-- You can set logging level to filter out log messages. 
-- You can set a hook function to be called after each log.
+- You can set output
+- You can set internal error output (slog writes Log method's errors to internal error output instead of returning them.)
+- You can set time format and prefixes
+- You can set logging level to filter out log messages
+- You can set a hook function to be called after each log
 
 **log** isn't the fastest logging solution, but **log** is efficient while being customizable. Please see [benchmark tests](https://github.com/ermanimer/log#benchmark-tests).
 
 # Usage
+
 ```go
 package main
 
 import (
 	"os"
 
-	"github.com/ermanimer/log"
+	"github.com/ermanimer/log/v2"
 )
 
 func main() {
 	// create a new logger instance with output and default parameters
-	l := log.NewLogger(os.Stdout)
+	l := log.NewLogger()
 
 	// log a message
 	l.Debug("this is a debug message")
@@ -40,36 +46,60 @@ func main() {
 ```
 
 **Output:**
+
 ```bash
 2021-06-07T16:46:26+03:00 debug this is a debug message
 2021-06-07T16:46:26+03:00 debug this is a formatted debug message
 ```
 
 # Logging Levels
+
  - Debug
  - Info
  - Warning
  - Error
  - Fatal
 
 # Default Parameters:
+
 | Parameter | Value |
 |:----------|:-----:|
-| Time Format | RFC3339 |
-| Debug Prefix | debug |
-| Info Prefix | info |
-| Warning Prefix | warning |
-| Error Prefix | error |
-| Fatal Prefix | fatal |
-| Logging Level | Debug |
+|Output|os.Stdout|
+|Internal Error Output|os.Stderr|
+|Time Format|RFC3339|
+|Debug Prefix|debug|
+|Info Prefix|info|
+|Warning Prefix|warning|
+|Error Prefix|error|
+|Fatal Prefix|fatal|
+|Logging Level|Debug|
+
+# Set Output
+
+```go
+l.SetOutput(os.Stderr)
+```
+
+# Set Internal Error Output
+
+```go
+l.SetOutput(io.Discard)
+```
+
+# Set Logging Level
 
+```go
+l.SetLoggingLevel(InfoLevel)
+```
 
 # Set Time Format
+
 ```go
 l.SetTimeFormat(time.RFC3339Nano)
 ```
 
 # Set Prefixes
+
 ```go
 l.SetDebugPrefix("DEB")
 l.SetInfoPrefix("INF")
@@ -78,21 +108,18 @@ l.SetErrorPrefix("ERR")
 l.SetFatalPrefix("FAT")
 ```
 
-# Set Logging Level
-```go
-l.SetLoggingLevel(InfoLevel)
-```
-
 # Set Hook Function:
+
 ```go
 l.SetHookFunction(func(prefix, message string) {
-  //filter messages with prefix and capture for Sentry.io
-  //...
+  //you can filter messages with prefix and capture for Sentry.io
 })
 ```
 
 # Benchmark Tests
+
 **Test Codes:**
+
 ```go
 func BenchmarkDebug(b *testing.B) {
 	// create logger
@@ -119,15 +146,16 @@ func BenchmarkDebugf(b *testing.B) {
 }
 ```
 **Results:**
+
 | Function | Time | Bytes Allocated | Objects Allocated |
 |:---------|:----:|:---------------:|:-----------------:|
-| Debug | 410.7 ns/op | 4 B/op | 1 allocs/op |
-| Debugf | 408.7 ns/op | 4 B/op | 1 allocs/op |
-| Info | 404.0 ns/op |  4 B/op | 1 allocs/op |
-| Infof | 403.9 ns/op | 4 B/op | 1 allocs/op |
-| Warning  | 407.0 ns/op | 4 B/op | 1 allocs/op |
-| Warningf | 409.4 ns/op | 4 B/op | 1 allocs/op |
-| Error | 404.6 ns/op | 4 B/op | 1 allocs/op |
-| Errorf | 406.2 ns/op | 4 B/op	| 1 allocs/op |
-| Fatal |  402.1 ns/op | 4 B/op | 1 allocs/op |
-| Fatalf | 406.0 ns/op | 4 B/op |	1 allocs/op |
+|Debug|410.7 ns/op|4 B/op|1 allocs/op|
+|Debugf|408.7 ns/op|4 B/op|1 allocs/op|
+|Info|404.0 ns/op|4 B/op|1 allocs/op|
+|Infof|403.9 ns/op|4 B/op|1 allocs/op|
+|Warning|407.0 ns/op|4 B/op|1 allocs/op|
+|Warningf|409.4 ns/op|4 B/op|1 allocs/op|
+|Error|404.6 ns/op|4 B/op|1 allocs/op|
+|Errorf|406.2 ns/op|4 B/op|1 allocs/op|
+|Fatal|402.1 ns/op |4 B/op|1 allocs/op|
+|Fatalf|406.0 ns/op|4 B/op|1 allocs/op|

go.mod

@@ -0,0 +1,3 @@
+module github.com/ermanimer/log/v2
+
+go 1.17