Patch: Add Process.chdir to change working directory, exposing libuv uv_chdir

[Josh Goebel]

This work has been done already for wren-console (PR #8). Should be a clean patch here as well if we'd like to add it. I think it's useful enough to have in the core CLI library.

Example:

import "os" for Process
Process.chdir("work/tmp/basic")