Add README.md

README.md

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+log
+================
+
+[![Go Report Card](https://goreportcard.com/badge/github.com/subchen/gstack/log)](https://goreportcard.com/report/github.com/subchen/gstack/log)
+[![GoDoc](https://godoc.org/github.com/subchen/gstack/log?status.svg)](https://godoc.org/github.com/subchen/gstack/log)
+
+Logging package similar to log4j for the Golang.
+
+* Support dynamic log level
+* Daily log file output
+* Fixed size log file ouput
+* Output console and file all at once
+* Output full stack
+* Output goroutinue id to console
+* Output colorized level to console
+
+Installation
+---------------
+
+```bash
+$ go get github.com/subchen/gstack/log
+```
+
+Usage
+---------------
+
+### Default log to console
+
+```go
+import (
+    "github.com/subchen/gstack/log"
+)
+
+func main() {
+    log.Debug("Some Message ...")
+    log.Error("error = %v", errors.New("some error"))
+
+    // dynamic set level
+    log.SetLevel(log.INFO)
+
+    log.Debug("cannot output debug message")
+    log.Info("can output info message")
+}
+```
+
+### Output to file
+
+```go
+import (
+    "github.com/subchen/gstack/log"
+)
+
+func main() {
+    log.SetWriter(&log.FixedSizeFileWriter{
+        Name:     "/tmp/test.log",
+        MaxSize:  10 * 1024 * 1024, // 10m
+        MaxCount: 10,
+    })
+
+    log.Debug("x = %v", "123")
+}
+```
+
+### We have four writers for use
+
+```go
+// Create log file if file size large than fixed size (10m)
+// files: /tmp/test.log.0 .. test.log.10
+&log.FixedSizeFileWriter{
+    Name:     "/tmp/test.log",
+    MaxSize:  10 * 1024 * 1024, // 10m
+    MaxCount: 10,
+}
+
+// Create log file every day.
+// files: /tmp/test.log.2016-01-02
+&log.DailyFileWriter{
+    Name: "/tmp/test.log",
+}
+
+// Create log file every process.
+// files: /tmp/test.log.20160102_150405
+&log.AlwaysNewFileWriter{
+    Name: "/tmp/test.log",
+}
+
+// Output to multiple writes
+&log.CompositeWriters{
+    os.Stdout,
+    &log.DailyFileWriter{
+        Name: "/tmp/test.log",
+    }
+    //...
+}
+```
+
+### New log instance
+
+```go
+import (
+    "github.com/subchen/gstack/log"
+)
+
+func main() {
+    logger := log.New(&log.DailyFileWriter{
+        Name: "/tmp/test.log",
+    })
+
+    logger.Debug("i = %d", 99)
+}
+```
+
+### Output stack
+
+You can use `log.Fatal(...)` to output full stack
+
+```
+21:04:32.884 main FATAL logger_test.go:24 this is a fatal message
+	at /go/src/github.com/subchen/gstack/log/logger_test.go:24 (0x81db3)
+	at /usr/local/Cellar/go/1.5.2/libexec/src/testing/testing.go:456 (0x786c8)
+	at /usr/local/Cellar/go/1.5.2/libexec/src/runtime/asm_amd64.s:1721 (0x59641)
+```
+
+### Log format
+
+```
+# time pid [name] [gid] level file:line message
+2016-02-10 19:33:02.587 12345 main 987 INFO fixed_size_file_writer_test.go:16 message ...
+```
+
+* `log.SetTimeLayout("2006-01-02 15:04:05.999")` customize time format
+* `log.SetName("main")` add a name in log for indicate process
+* `log.EnableGoroutineId(true)` to output goroutine id
+* `log.EnableLongFileFormat(true)` to output long file name
+* `log.EnableColorizedLevel(true)` to output colorful message to console
+
+### API on godoc.org
+
+https://godoc.org/github.com/subchen/gstack/log

doc.go

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+// Logging package similar to log4j for the Golang.
+package log