Added gui, mainmenu and hud for ingame stats

CMakeLists.txt

include/constants.h

include/game.h

include/pacman.h

include/renderer.h

include/ui.h

src/constants.cpp

src/game.cpp

src/imgui/.editorconfig

src/imgui/.gitattributes

src/imgui/.github/issue_template.md

src/imgui/.github/pull_request_template.md

src/imgui/.github/workflows/build.yml

src/imgui/LICENSE.txt

src/imgui/imconfig.h

src/imgui/imgui.cpp

src/imgui/imgui.h

src/imgui/imgui_demo.cpp

src/imgui/imgui_draw.cpp

src/imgui/imgui_impl_glfw.cpp