New Matrix benchmarks after merging #186

|                     | add1        | add2      | mul1     | mul2    |
| -------------    |:------------:| ----------:|:--------   |:----------|
| CSymPy     |      7         |     6        |       90   |     44    |  
| GiNaC         |     4          |     3        |      26    |   27      |

All the times are in `microseconds`.