Merge pull request #19 from kc1212/develop

remoted c++11 only code for better portability
Merge pull request #20 from kc1212/develop

updated cmake and travis for SDL2_ttf
Merge pull request #21 from kc1212/develop

fixing travig (SDL2_ttf)
fixing travis (SDL_ttf)
Merge branch 'develop' of https://github.com/stephenyao/flappy_bear into develop