Remove recursive Makefile within cuIBM source folder

This Makefile compiles and links cuIBM code.

Instead of generating static libraries, the object files are stored in the `build` directory.

Unit-tests have been moved outside the `src` folder.

Doxygen configuration file has been moved to new `doc` folder.

@anushkrish , what do you think about having just one Makefile for `cuIBM`? Do you have any improvement to add to the process?