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/Path.h

@@ -28,7 +28,6 @@
 #ifndef INCLUDED_PATH
 #define INCLUDED_PATH
 
-#include <iostream>
 #include <vector>
 #include <string>
 
@@ -42,6 +41,7 @@ public:
 
   Path& operator= (const Path&);
   bool operator== (const Path&);
+  Path& operator+= (const std::string&);
   operator std::string () const;
 
   std::string name () const;