Reduce allocation and unnecessary layers (#822)

The focus here was to **reduce allocation in TCP parser** but speed may have hopeful improved too!
pool no longer use map's key of **string** it uses **uint64**
**Benchmarks** was revamped to be more clear
if you want to compare these results copy the benchmark in tcp/bench_test.go@reduce-allocation to tcp/bench_test.go@master:

**before(master)**:
```
BenchmarkPacketParseAndSort-4         	 1000000	      1006 ns/op	      64 B/op	       2 allocs/op
BenchmarkMessageParserWithoutHint-4   	     625	   1772309 ns/op	      1000 packets/op	  419096 B/op	   10045 allocs/op
BenchmarkMessageParserWithHint-4      	      74	  14969926 ns/op	      1000 chunks/op	      1002 packets/op	  450992 B/op	   10126 allocs/op
```

**After(this branch)**:
```
BenchmarkPacketParseAndSort-4         	 1267662	       941 ns/op	      64 B/op	       2 allocs/op
BenchmarkMessageParserWithoutHint-4   	    2256	    523474 ns/op	      1000 packets/op	  243530 B/op	    1037 allocs/op
BenchmarkMessageParserWithHint-4      	      80	  13990955 ns/op	      1000 chunks/op	      1002 packets/op	  268609 B/op	    1099 allocs/op

```

byteutils/byteutils.go

@@ -2,7 +2,6 @@
 package byteutils
 
 import (
-	"reflect"
 	"unsafe"
 )
 
@@ -48,9 +47,6 @@ func Replace(a []byte, from, to int, new []byte) []byte {
 }
 
 // SliceToString preferred for large body payload (zero allocation and faster)
-func SliceToString(buf *[]byte, s *string) {
-	bHeader := (*reflect.SliceHeader)(unsafe.Pointer(buf))
-	sHeader := (*reflect.StringHeader)(unsafe.Pointer(s))
-	sHeader.Data = bHeader.Data
-	sHeader.Len = bHeader.Len
+func SliceToString(buf []byte) string {
+	return *(*string)(unsafe.Pointer(&buf))
 }

byteutils/byteutils_test.go

@@ -32,9 +32,10 @@ func TestReplace(t *testing.T) {
 }
 
 func BenchmarkStringtoSlice(b *testing.B) {
-	b.StopTimer()
-	buf := make([]byte, b.N)
-	b.StartTimer()
-	s := new(string)
-	SliceToString(&buf, s)
+	var s string
+	var buf [1 << 20]byte
+	for i := 0; i < b.N; i++ {
+		s = SliceToString(buf[:])
+	}
+	_ = s // avoid gc to optimize away the loop body
 }