fixed README due to methods isNull() and isEmpty()
have gotten out from class Matrix
added function defineSignForElement
fixed: included <cmath> for pow()
added case Matrix3x3 to test GetUpperTriangularMatrix
added case SeveralCases to test DefineSignForElement
added case Matrix4x4 to test CalculateDeterminantViaTriangularMatrix
moved function defineSignForElement to class ClassicDeterminantCalculator
refactoring
changed type of returned value of getElement() to const ELEMENT_TYPE&
added method getElementReference()
added test for method getElementReference()
added methods at() and at() const
added case Matrix3x3 to test MatrixAtMethod
changed name of case SeveralCases at test MatrixGetElementReference to GetElement1x0InMatrix3x3
added case ConstMatrix3x3
added template method getMinorForElement()
added three tests for getMinorForElement()
added methods throwExceptionIfRowIndexIsWrong() and
throwExceptionIfColumnIndexIsWrong()
added tests for methods throwExceptionIfRowIndexIsWrong() and
throwExceptionIfColumnIndexIsWrong()
added checks for indexes at method getMinorForElement()