Added FreeFileSync file extension to .gitignore.
Added the DirectXTK SDK back into the repository. This will make the project easier for others to pull and run.
Moved MakeSpriteFont.exe and XWBTool.exe inside the DirectXTK SDK. Made more sense to me to keep all DirectXTK stuff in the references/DirectXTK directory.
Reorganized entries in .gitignore to facilitate temporary modifications. Specifically, easy committing of updates to references.