Code of Conduct, mk II

Changes from the original:

* does not include contribution policy and governance documents
* explicitly defines the scope of the Node.js Project
* explicitly defines harrassment
* explicitly defines consequences
* adds grievance policy
* introduces notion of specific points of contact for abuse reports; still need a list of actual names to go into the policy
* adds credit and link to the npm, Inc. Code of Conduct
* incorporates community feedback

Please limit discussion on this issue to the Code of Conduct itself:
  * ambiguous or confusing wording
  * typos
  * contradictions
  * scope of the document

Discussion of the necessity or relevance of a Code of Conduct for the Node.js Project is irrelevant to this PR, and should be conducted elsewhere.
Should it matter who asks you to stop something? If someone asks you to stop doing something that is actively making them uncomfortable, are you in the habit of continuing that behavior? If you are, it might be best if you reassessed your perspectives. It is entirely possible to continue doing something constructive in most instances while still comply with a person's request to cease some type of interaction.