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.cpp

@@ -112,3 +112,40 @@ void Timer::subtract (unsigned long value)
 }
 
 ////////////////////////////////////////////////////////////////////////////////
+HighResTimer::HighResTimer ()
+{
+  _start.tv_sec = 0;
+  _start.tv_usec = 0;
+
+  _stop.tv_sec = 0;
+  _stop.tv_usec = 0;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+HighResTimer::~HighResTimer ()
+{
+}
+
+////////////////////////////////////////////////////////////////////////////////
+void HighResTimer::start ()
+{
+  gettimeofday (&_start, NULL);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+void HighResTimer::stop ()
+{
+  gettimeofday (&_stop, NULL);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+double HighResTimer::total () const
+{
+  if (_stop.tv_sec > 0 || _stop.tv_usec > 0)
+    return (_stop.tv_sec  - _start.tv_sec) +
+           (_stop.tv_usec - _start.tv_usec) / 1000000.0;
+
+  return 0.0;
+}
+
+////////////////////////////////////////////////////////////////////////////////