Makefile not tracking header files

[Testspieler09]

Currently the makefile does not track the header files. That means that if you compile the program with make and then change something in a header file and recompile it with make it won't do anything as it only tracks the .cpp files. The workaround is to make clean and then make again.

If anyone wants to adjust the header file, so it recompiles the program when a header file changed please feel free to do so.

It is a very good and easy first issue. If you do it please remove the caution label in the README.md

[Testspieler09]

It makes a lot more sense to switch to cmake as this program is meant to be cross platform.