Feature: Handle / test symlinks.

[ryan-roemer]

See: FormidableLabs/serverless-jetpack#142

• Basic tests for how symlinks are resolved (probably in a monorepo with a lib/package1|2 and functions/packageA|B|C, etc.

[leemhenson]

I added a big old monorepo-with-symlinks test case in my fork as documented here: FormidableLabs/serverless-jetpack#142 (comment)

One of the things to catch is that scoped packages have / in the middle (e.g. @npm/cli) which can throw off your path wrangling unless you're careful (e.g. not all package.jsons are at node_modules/*/package.json).