[iMathDrills 1.1 Release]

[iMathDrills 1.1 PreRelease]
Change "difficulty" from "digit".
Fine-tuning the degree of difficulty.(=Difficulty2)
Add a high degree of difficulty.(=Difficulty4)

・iPad Support
・iOS5.1 Support
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桁数を難易度に変更し、難易度1(簡単)～4(難しい)まで追加、
難易度の微調整とより難しい難易度を追加

・iPad Support
・iOS5.1 Support