Merge pull request #9 from L4D15/res-management

Added `ResourceManager` class to handled game's assets.
Added libraries as git submodules.
Updated libraries.

SDL2 will be no longer deployed with the engine.
Added Linux support.
Merge branch 'libs'
Advanced HEAD of submodules.
Added Windows support.
Merge pull request #10 from L4D15/windows

Added Windows support.
Updated README with the change in Artemis-Cpp and JsonCpp handling.

Now those libraries are used as subprojects in CMake so they don't need additional steps to compile and link them. These change has been stated in the README.
Cleaned up not necesary cmake modules.
Merge pull request #11 from L4D15/doc

Doc
Created CollisionBox class.
Added Visual Studio support.
Cleaned code.
Merge pull request #13 from L4D15/visualStudio

Visual studio
Created basic structure for collision box.
Changed format for all methods and functions.
Merge pull request #14 from L4D15/formatting

Formatting
More formatting.
Fixed resources paths in ResourceManager.