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.
I do as well. Unfortunately, the behavior I witnessed yesterday on twitter was **not** at all in line with what was written here. 

The behavior yesterday was:
- not welcoming
- not safe
- people were not kind and courteous
- people were mean and rude
- people mocked me and others.
- people did not respect my different opinion
- my pull request was belittled

Multiple people were involved. I won't name names. Some of you are here reading this thread. You know who you are.
Seriously, yesterday was a complete and utter failure of many people in the community to follow the CoC and yet there has been not one comment from the leadership addressing this.  

** Retweeting inappropriate behavior that violates the CoC is tantamount to violating the CoC since that comment is now shared on your own timeline as a comment you agree with.