Added equality test

I have added a test for equality of two matrices that are empty. The
next step is implement checkings to compare all different topologies of
matrices that can be represented with the matrix class.
Implemented part of the equality method

Matrices are compared by rows and by columns.
I forgot to add a file :P
Completed matrix equality

The next step is to refactor the write method to output a matrix in a
correct way.
Fixed matrix equality

There were two problems in Matrix class:
1. Indexing was implemented in an sloppy way. That is my fault... :(
2. Equality was not correct.

If implemented both mechanisms but they have to ve reviewed.
- Equality is not efficient (in time).
- Indexing may be refectored to make it a bit more clear.