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 brianc -r node-postgres -f CHANGELOG.md -a -v`

Please let me know if you need any help adding it to your deploy script. If there are any improvements you'd like to see in the script please feel free to open an issue :) Thanks!