hxx extension causes cc1plus warnings

[gamedev-mario]

Compiling the application causes warnings for every header file with the extension .hxx. The warnings look like this:

cc1plus: warning: /home/badrmari/personal/software/IsometricEngine/src/engine/cell.hxx: not a directory

I am running Ubuntu 16.04 and using gcc version 6.4.0 with CLion 2018 v1.3 as my IDE.

Refactoring the header files to have a .hpp extension instead of .hxx takes care of the warnings. If you would like, I could submit a pull request with the change. If you agree with the change, you may also want to change cxx to cpp to be consistent, though gcc does not complain about the cxx extension.

[SimplyLiz]

The problem is not with the cxx extension, but with the "globbed" header files used wrongly in include_directories()
I ignored that warning until now, because the cmake system is due to some refactoring anyway. I think ill tackle #9 next week.