Refactoring and specified requirements.

README.md

src/main/java/ee/ut/cs/gitlab/maikov/VariableName.java

...cs/gitlab/maikov/exceptions/ImpossibleStateException.java

...t/cs/gitlab/maikov/exceptions/InvalidMatrixException.java

...s/gitlab/maikov/exceptions/InvalidReductionException.java

...ain/java/ee/ut/cs/gitlab/maikov/expressions/Addition.java

.../java/ee/ut/cs/gitlab/maikov/expressions/Determinant.java

...ain/java/ee/ut/cs/gitlab/maikov/expressions/Division.java

...n/java/ee/ut/cs/gitlab/maikov/expressions/Expression.java

...a/ee/ut/cs/gitlab/maikov/expressions/MatrixInversion.java

...a/ee/ut/cs/gitlab/maikov/expressions/MatrixTranspose.java

.../java/ee/ut/cs/gitlab/maikov/expressions/MatrixValue.java

...va/ee/ut/cs/gitlab/maikov/expressions/Multiplication.java

src/main/java/ee/ut/cs/gitlab/maikov/expressions/Number.java

.../java/ee/ut/cs/gitlab/maikov/expressions/Subtraction.java

src/main/java/ee/ut/cs/gitlab/maikov/expressions/Value.java

src/test/java/ExpressionTest.java