Update README.md
Merge pull request #75 from ReEmM/patch-1

Update README.md
fix #76, we now can use cmd+q to exit application
refactor window related code into windowManager
Merge pull request #77 from EragonJ/bug-76

fix #76, we now can use cmd+q to exit application
Merge pull request #78 from EragonJ/refactor/window-manager

refactor window related code into windowManager
added loading status bar