decrease build times for pack command

[fivetanley]

We can reuse the tarball and append new files (node binaries in this case) instead of compressing/extracting multiple times. This prevents un-necessary copying of files in the built tarball.

We can also build all targets in parallel in the following way:

• Download Node.js versions for targets in parallel instead of serially
• Use workerpool to create gzip files in parallel
• Run all xz compression with maximum available threads. xz has supported multicore computation since 5.2 (2014).
• Like gzip, run all xz compression in parallel instead of waiting for each target to build.

Running this in the Heroku CLI produced identical tarballs in 65% amount of time (~111s seconds vs ~344 seconds before this change). It's likely even a bit faster since I was running it locally which has some boot-up time due to ts-node compiling typescript at runtime.

This file brings in the tar dependency. This dependency is maintained by the npm team and is also cross-platform. This gets us quite a bit closer to allow building OClif CLIs on windows!