Zero-size Matrices

Is there an easy way to create matrices with zero rows or zero columns or both? This would be really useful in some cases.

At the moment, when I try to create such a matrix with 
```python
>>> A = LLSparseMatrix(nrow=0, ncol=5)
```
I get an error that size_hint must be greater than zero. (This happens even when I do not explicitly set the size_hint argument.)