BUG: fix zero initialization with subarray dtypes

closes #3724
Merge pull request #3725 from juliantaylor/fix-subarray-zeros

BUG: fix zero initialization with subarray dtypes
DOC: Make savez_compressed show up in the documentation.

Closes #3708.
Merge pull request #3736 from charris/add-savez_compressed-to-docs

DOC: Make savez_compressed show up in the documentation.