* Fix 404 and update latest version

Instead of throwing ErrInvalidDir, we try to create a directory that is
specified in the options. We throw an error only if we cannot create the
directory for some reason.

Fixes #312.

Add a ValueCopy function to avoid deadlocks in long running iterations.
Write Item::Value to a passed in byte slice.

This change fixes segmentation faults on Arm v7.

From https://golang.org/pkg/sync/atomic/:

> On both ARM and x86-32, it is the caller's responsibility to arrange
for 64-bit alignment of 64-bit words accessed atomically. The first word
in a variable or in an allocated struct, array, or slice can be relied
upon to be 64-bit aligned.

Had to modify a couple of tests to get them to pass.

Fixes #311.