Ignore specific module ids

[martinandert]

I've waited nearly 2 months for PR #75 to be finished. So here is my attempt on it.

This also fixes the relativize problem described in one of the comments of #75.

As an extra, this PR adds two new CLI flags:

--ignore-dependencies   Ignore required modules that are defined as dependencies in package.json
--ignore-node-core      Ignore required modules that are Node core modules ('fs', 'events', etc.)

Cherry-pick as much as your heart desires.