Add all .hpp files in CMakeLists.txt

[Dead-Deus]

it may be a matter of taste, but I think it's right

set(

        # Add all .hpp files, because in project structure they are hidden  

    src/LightingArea.cpp
    src/LightSource.cpp
    src/RadialLight.cpp
    src/DirectedLight.cpp
    src/Line.cpp
    src/Polygon.cpp
    src/Color.cpp
    src/VertexArray.cpp
    src/Constants.cpp

)

[MiguelMJ]

If more people think the same, I'll accept a pr with this change. For now, I'm leaving it as it is. Thank you @Dead-Deus 😄

[MiguelMJ]

Done in #24