added os.path functionality (limited subset)

Exposed a limited set of function from os.path (most of those which rely on pur
string processing have been implemented).  These have been added in an
architecture specific manner to match the python implementation. (I.e., join on
windows uses '\', and joing on linux uses '/'.  The python 2.6 implementation
were used as reference, and for unit test validation.

Author: jeremyselan

Makefile

@@ -20,5 +20,5 @@ clean:
 .PHONY: test
 test:
 	$(RM) -fr test
-	$(CXX) pystring.cpp test.cpp $(CXXFLAGS) -o test
+	$(CXX) pystring.cpp test.cpp $(CXXFLAGS) -DPYSTRING_UNITTEST=1 -o test
 	./test