Matrix Class is missing the __repr__() special method and therefore can't be displayed

Please consider adding the `__repr__` special method to the Matrix Class. Something like this:

```python
def __repr__(self):
result = ''
for r in range(4):
for c in range(4):
result += str(self.__getitem__((r,c)))
if c!=3:
result += ', '
result += '\n'
return result
```
Being able to display the matrix helps with debugging (for example, trying to determine if the rotate methods use radians or degrees).