Adding squeeze

Would be nice to have a wrapper for squeeze.

Without squeeze, matmul usage is quite limited because if will fail for all slices of bigger matrices. Example:

```
import arrayfire as af
x = af.constant(0, 10, 5, 5, dtype=af.Dtype.f64)
af.matmul(x[0,:,:],x[1,:,:]) # will fail because only matrices with two dimensions are allowed
```

No files or tests are named. Start by locating the Python wrapper for matmul and the binding pattern for ArrayFire's squeeze operation, then reproduce the provided af.constant and af.matmul example. Done means a squeeze wrapper is available and the sliced arrays can be used successfully with matmul.

Escrita pelo modelo de indexação a partir do texto da issue.