Show benchmarking for array combine stuff

[elidoran]

I made this PR separate from #185 because it's not my intent to add this stuff to master. Instead, I'm providing it just to mess with in its own branch.

Provides a new directory, benchmark/, with a script to benchmark different array combination implementations.

Adds dev dependencies:

1. benchmark
2. console.table
3. comma-number

Run benchmark via:

node benchmark/arraying.js

[ljharb]

fwiw, I'm happy to merge this into the project as long as all the important scripts can be run via npm run-script. no big deal either way.

[ljharb]

comma last, please :-)