fix several bugs and add support for mobile

• fix several bugs about score:
  1. score is added twice when player quits.
  2. score doesn't run.
  3. total score doesn't clear when creating another game.
  4. prev button works incorrectly.
• improvement:
  1. eating skull should die.
  2. eating fruit plays audio.
  3. remove annoying audio of rank scene.
• test on Meizu MX 2 and modify UI.
• add youmi advertisement.
• add introduction and redesign logo.
• add exit button.

Add hint and fix bugs

• add hint bar.
• fix bug of appearing white line between two pictures when scrolling background.

Add rotating direction functionality. Fix several bugs.

• prev and next buttons can hide when no more content.
• improve help scene UI design to better support different resolutions.
• fix end scene's bug of treating place holder as player's name when player directly hits enter button.
• now even if player doesn't complete a stage, the score earned in this stage can also be added up to total score.
• fix rank scene bug: need to click prev button to show result.
• modify several properties to make them easier to distinguish and catch.
• add shoot direction rotating functionality, to let player control shoot direction.