Enable _.range() to accept a 0 for step

Enable `_.range()` to accept a `0` for `step`, for initializing arrays such as `[0, 0, 0, 0, 0]`, `[-1, -1, -1, -1, -1]`, useful in many use cases with inconsistent/morphing object arrays.
Merge pull request #327 from stereokai/master

Enable _.range() to accept a 0 for step.