Bumped minimum supported version to 0.8

Tests pass with 0.4 and 0.6, but 0.6 breaks coverage reporter. Frankly,
I'm too lazy to to anything about it. At the same time, I want that
coverage report without the need to run `make coverage` every time,
since I don't always have access to PC lately.

If someone finds a way to work around the problem - please do so, add
your name to contributors and copyright holders and send a pull request.
I'll be beyond grateful. For now though, please upgrade your node
version to 0.8 or higher.
Added basic test coverage for duration option code

TODO: Implement reddit endpoint expectations using nock
TODO: Bump version and release