Adds debug mode (part 1)

- Adds API to switch the gin's mode
- Log listening port
- Log routes

mode.go

@@ -0,0 +1,38 @@
+package gin
+
+import (
+	"os"
+)
+
+const GIN_MODE = "GIN_MODE"
+
+const (
+	DebugMode   string = "debug"
+	ReleaseMode string = "release"
+)
+const (
+	debugCode   = iota
+	releaseCode = iota
+)
+
+var gin_mode int = debugCode
+
+func SetMode(value string) {
+	switch value {
+	case DebugMode:
+		gin_mode = debugCode
+	case ReleaseMode:
+		gin_mode = releaseCode
+	default:
+		panic("gin mode unknown, the allowed modes are: " + DebugMode + " and " + ReleaseMode)
+	}
+}
+
+func init() {
+	value := os.Getenv(GIN_MODE)
+	if len(value) == 0 {
+		SetMode(DebugMode)
+	} else {
+		SetMode(value)
+	}
+}