Added code of conduct

This is largely based on the Contributor Covenant but with the list of
unacceptable behaviours updated according to the Rubinius CoC (as I feel
the latter is more explicit/accurate/better).

COC.md

@@ -0,0 +1,56 @@
+# Contributor Code of Conduct
+
+As contributors and maintainers of this project, and in the interest of
+fostering an open and welcoming community, we pledge to respect all people who
+contribute through reporting issues, posting feature requests, updating
+documentation, submitting pull requests or patches, and other activities.
+
+We are committed to making participation in this project a harassment-free
+experience for everyone, regardless of level of experience, gender, gender
+identity and expression, sexual orientation, disability, personal appearance,
+body size, race, ethnicity, age, religion, or nationality.
+
+Examples of unacceptable behavior by participants include:
+
+* Violence, threats of violence or violent language directed against another
+  person.
+* Sexist, racist, homophobic, transphobic, ableist or otherwise discriminatory
+  jokes and language.
+* Posting or displaying sexually explicit or violent material.
+* Posting or threatening to post other people’s personally identifying
+  information ("doxing").
+* Personal insults, particularly those related to gender, sexual orientation,
+  race, religion, or disability.
+* Inappropriate photography or recording.
+* Inappropriate physical contact. You should have someone’s consent before
+  touching them.
+* Unwelcome sexual attention. This includes, sexualized comments or jokes;
+  inappropriate touching, groping, and unwelcomed sexual advances.
+* Deliberate intimidation, stalking or following (online or in person).
+* Advocating for, or encouraging, any of the above behavior.
+* Sustained disruption of community events, including talks and presentations.
+
+Project maintainers have the right and responsibility to remove, edit, or reject
+comments, commits, code, wiki edits, issues, and other contributions that are
+not aligned to this Code of Conduct, or to ban temporarily or permanently any
+contributor for other behaviors that they deem inappropriate, threatening,
+offensive, or harmful.
+
+By adopting this Code of Conduct, project maintainers commit themselves to
+fairly and consistently applying these principles to every aspect of managing
+this project. Project maintainers who do not follow or enforce the Code of
+Conduct may be permanently removed from the project team.
+
+This Code of Conduct applies both within project spaces and in public spaces
+when an individual is representing the project or its community.
+
+Instances of abusive, harassing, or otherwise unacceptable behavior may be
+reported by contacting a project maintainer at <yorickpeterse@gmail.com>. All
+complaints will be reviewed and investigated and will result in a response that
+is deemed necessary and appropriate to the circumstances. Maintainers are
+obligated to maintain confidentiality with regard to the reporter of an
+incident.
+
+This Code of Conduct is adapted from the Contributor Covenant
+(<http://contributor-covenant.org>), version 1.3.0, available at
+<http://contributor-covenant.org/version/1/3/0/>.

CONTRIBUTING.md

@@ -4,6 +4,12 @@ Everybody is more than welcome to contribute to Oga, no matter how small the
 change. To keep everything running smoothly there are a bunch of guidelines that
 one should follow.
 
+## Code of Conduct
+
+The code of conduct ("CoC") can be found in the file "COC.md". Everybody
+participating in this project must adhere to the rules and guidelines stated in
+this CoC.
+
 ## General
 
 * When changing code make sure to write RSpec tests for the changes.