refactoring
Add support for answer parsing
Merge branch 'master' of https://github.com/anphoenix/eteacher

Conflicts:
	eteacher/src/com/phoenix/eteacher/util/MathUtils.java
	eteacher/src/com/phoenix/eteacher/util/SampleQuestions.java
	eteacher/test/com/phoenix/eteacher/util/CompareExpressionTest.java