Git commit log style guidelines

This contains a first pass at git commit log message style guidelines.
It is simplified from the overly verbose and pedantic:
http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html
I would love to add examples of good and bad style here.

Here are some examples I might include:

----
Bad example:
```
Refactored all network code to use Netty
```

The above would be a bad git commit log because it does not have a body outlining the major types of changes (and why they were made) along with potential implications of such a likely massive change. You should not accept such a git commit log during review.

Good example (small scope):
```
Update README.md Contribution section
```

Assuming the above describes the changes fully, this is a very acceptable git commit message. No need to for many small changes to have a commit message body after the empty line.

Good example (larger scope):
```
Refactor network layer to use Netty 4.x APIs

The following components have been migrated from Netty 3.x to 4.x:
* Cluster state communication and acknowledge
* Request delegation to node owning shard
* ...

Implications of this are that the test suite had to be radically refactored too.
```

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