Bugfix release

Finally fixed sparse matrix support, so that this code is verified to work:

import numpy as np
import loompy
import scipy.sparse as sparse
filename = "test.loom"
matrix = sparse.coo_matrix((100, 100))
row_attrs = { "SomeRowAttr": np.arange(100) }
col_attrs = { "SomeColAttr": np.arange(100) }
loompy.create(filename, matrix, row_attrs, col_attrs)

(CSR, CSC and COO matrices are all supported and tested).

Also updated the docs with the example above.