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.
That's on purpose. The CoC doesn't define a justice code or even any kind of binding mediation. It outlines a set of values and processes by which the Node.js community can ensure that it is taking care of itself and is working towards creating an inclusive, healthy, and productive development community. As such, when things do go pear-shaped, the project will need to decide on a case-by-case basis what's appropriate. "Appropriately" in this case implies that whatever resolution the project comes up with will be in line with the project's stated values and goals.