Add serialization to SubMatrix
Add empty constructor to SubMatrix
Add equals and hashCode to SubMatrix
Add Spock specification framework.

Add some unit tests for the SubMatrix class
Add some basic tests for Operations class
Move matrix sum logic to its own method
Add tests for the sum of matrices
Move matrix product to its own method
Add test case for product and fix bug

Fix index bug in matrix multiplication
Add .travis.yml

Start using continous integration offered by Travis-CI