Create changelog based on pull requests

I created a simple tool here https://github.com/lalitkapoor/github-changes.

To use it you can:
`npm install -g github-changes`

This was the command used to generate the changelog:
`github-changes -o mikeal -r request -a -v -f CHANGELOG.md`

just FYI, code is a little messy in github-changes right now. I wanted to hack out something quickly and it was my first time playing with promises - so please let me know if you run into any issues. I'll do some cleaning up later.

Please let me know if you need any help adding it to your deploy script.

addresses #771