Extending JavaScript's slice

[jakirkham]

In the docs, it says slice doesn't support steps because JavaScript doesn't. Though it looks like there is a proposal to add slices with steps to JavaScript. In the interim, this gist has a simple slice implementation. Also this repo implements slice support with custom objects. They discuss this work in this blogpost.

ref: http://pscript.readthedocs.io/en/latest/intro.html#support