1. moved factory to main namespace

2. common.h

include/c11log/common.h

+#pragma once
+
+namespace c11log
+{
+
+using log_clock = std::chrono::system_clock;
+namespace level
+{
+typedef enum
+{
+    TRACE,
+    DEBUG,
+    INFO,
+    WARNING,
+    ERROR,
+    CRITICAL,
+    FATAL,
+    NONE = 99
+} level_enum;
+
+static const char* level_names[] { "trace", "debug", "info", "warning", "error", "critical", "fatal" };
+inline const char* to_str(c11log::level::level_enum l)
+{
+    return level_names[l];
+}
+} //level
+} //c11log