add drafts of first two notebooks

I wanted to send along a draft so that you could comment on the style I'm taking.  Criticism welcome.
So, I'm assuming that you noticed that you *don't* get the identity matrix, or at least, it doesn't look like it:

```
In [8]: M*M.inv()
Out[8]:
⎡             1                         0          ⎤
⎢                                                  ⎥
⎢  ⎛  x⋅y       ⎞      y          x⋅y         1    ⎥
⎢y⋅⎜──────── + 1⎟ - ────────  - ──────── + ────────⎥
⎣  ⎝-x⋅y + 1    ⎠   -x⋅y + 1    -x⋅y + 1   -x⋅y + 1⎦
```

You have to call `simplify()` on it. 

Somewhat related, you have to call `simplify` on the determinant example above to get the actual determinant (`r**2`) (I see you subtitley did this for the determinant calculation below). 

How should we handle this? We probably just need to note that `simplify` does work on matrices and you may need to call it sometimes. 

Or was this all on purpose?