Add live tracing facility

Set NODESASS_TRACE enviroment variable
to any value to get lots of output.

binding.gyp

@@ -8,6 +8,7 @@
         'src/create_string.cpp',
         'src/custom_function_bridge.cpp',
         'src/custom_importer_bridge.cpp',
+        'src/debug.cpp',
         'src/sass_context_wrapper.cpp',
         'src/sass_types/boolean.cpp',
         'src/sass_types/color.cpp',

src/debug.cpp

@@ -0,0 +1,27 @@
+#include <stdio.h>
+#include <sstream>
+
+#include <uv.h>
+
+#include "debug.h"
+
+Log::Log() {} 
+
+std::ostringstream& Log::Get(TLogLevel level, void *p, const char *f, const char *filen, int lineno)
+{
+   os << "[NODESASS@" << uv_thread_self() << "] " << p << ":" << f << " " << filen << ":" << lineno << " ";
+   messageLevel = level;
+   return os;
+}
+std::ostringstream& Log::Get(TLogLevel level, const char *f, const char *filen, int lineno)
+{
+   os << "[NODESASS@" << uv_thread_self() << "] " << f << " " << filen << ":" << lineno << " ";
+   messageLevel = level;
+   return os;
+}
+Log::~Log()
+{
+   os << std::endl;
+   fprintf(stderr, "%s", os.str().c_str());
+   fflush(stderr);
+}

src/debug.h

@@ -0,0 +1,38 @@
+#ifndef NODE_SASS_DEBUG_H
+#define NODE_SASS_DEBUG_H
+
+#include <sstream>
+
+enum TLogLevel {logINFO, logTRACE};
+static TLogLevel LogReportingLevel = getenv("NODESASS_TRACE") ? logTRACE : logINFO;
+class Log
+{
+public:
+  Log();
+  virtual ~Log();
+  std::ostringstream& Get(TLogLevel level, void *p, const char *f, const char *filen, int lineno);
+  std::ostringstream& Get(TLogLevel level, const char *f, const char *filen, int lineno);
+public:
+protected:
+  std::ostringstream os;
+private:
+  Log(const Log&);
+  Log& operator =(const Log&);
+private:
+  TLogLevel messageLevel;
+};
+
+// Visual Studio 2013 does not like __func__
+#if _MSC_VER < 1900
+#define __func__ __FUNCTION__
+#endif
+
+#define TRACE() \
+  if (logTRACE > LogReportingLevel) ; \
+  else Log().Get(logTRACE, __func__, __FILE__, __LINE__)
+
+#define TRACEINST(obj) \
+  if (logTRACE > LogReportingLevel) ; \
+  else Log().Get(logTRACE, (obj), __func__, __FILE__, __LINE__)
+
+#endif