Fixed for-loop concurrency with store test

- helper.genPost now gets called multiple times
Examples + readme first attempt.
Single item get and example.
Store should return chunk instead of just key.
Fixes to store test

- updated store functions to use chunk instead of value
- refactor with some comments to clarify indexer keys
- named assertions in test
Removed 'index' separator from pri and sec indexes.
Tests refactor

- generator separated from teardown
- test-treedb modularized for multiple tests
Parameterized gen objects in test.
Test target.
Travis build file.
Fixes pending.