Code Cleanup

- Cmake was not updating HAVE_ST_BIRTHTIME.
- NIBBLER_FEATURE_DATE was not properly applied everywhere.
- FEATURE_COLOR was not properly set.
- Some source files failed to include cmake.h, and therefore were not properly
- Removed inefficient use of std::string::substr for guaranteed single character
  strings.
- Integrated Directory::cd.
- Integrated File::ctime, ::btime.
- Integrated Path::operator+.
- Integrated Nibbler::getDigit{2,4,6}.
- Integrated HighResTimer.
  enabling/disabling code.
- All Path objects now expanded internally to absolute form.
- Modified unit tests to accomodate absolute paths.
- Merged new nibbler.t.cpp tests.
- Made various methods const.
- Includes removed from some files, added to others.

src/Timer.h

@@ -31,6 +31,7 @@
 #include <string>
 #include <sys/time.h>
 
+// Timer is a scope-activated timer that dumps to std::cout at end of scope.
 class Timer
 {
 public:
@@ -52,6 +53,25 @@ private:
   unsigned long  _total;
 };
 
+// HighResTimer is a stop watch with microsecond resolution.
+class HighResTimer
+{
+public:
+  HighResTimer ();
+  ~HighResTimer ();
+  HighResTimer (const HighResTimer&);
+  HighResTimer& operator= (const HighResTimer&);
+
+  void start ();
+  void stop ();
+  double total () const;
+
+private:
+  struct timeval _start;
+  struct timeval _stop;
+};
+
+
 #endif
 
 ////////////////////////////////////////////////////////////////////////////////