Release Memento version 0.1.13.
Release Memento version 0.1.13.

 * Remove dead code.
 * Fix snapshot, mutator return unit test. See #105.
 * Return user return value from snapshot, mutator. Closes #105.
 * Fix store rename. Closes #106.
 * Create staging direction when writing out version.

Closes #107.

bigeasy/memento