Argument parsing.

		 * src/main.cc: Here.
Put the usage string function et the argument parsing in their own files.

	* src/main.cc: Use it.
	* src/utils.hh: Here.
	* src/utils.cc: Here.
	* CMakeLists.txt: Compile it.
Added the computation of the integral image.

	  * src/integralImage.hh: Here.
	  * src/integralImage.hxx: Here.
	  * src/main.cc: Use it.