#167 .hh header files

Files with .hh extensions should be considered as headers
like .h files by Dev-C++ when it generates its makefile. Else
one needs some time to understand what is going one when
the compiler complains about not knowing how to
build 'NameOfHeaderFile.o' if there is no
corresponding .cpp file.

In the same vein, syntax highlighting could by default be
enabled for .hh and .cc files. This is not important !