Added release.sh script to simplify release process

@drtriumph - I've created `release.sh` scripts for a lot of other repos and it's simplified the whole process for me. It also prevents us from making any stupid mistakes, such as forgetting to update the changelog or the `package.json` file. I went ahead and created a `release.sh` script for the firebase-tools repo as well.

Another note: I think we should create a git tag for each release, as we do with other repos. Then people can easily look through our releases on GitHub and quickly see how the code looked during a particular release. We also can add the changelog info to each release on GitHub. I added this to the manual tasks list which get printed at the end of the `release.sh` script. Feel free to chat with me offline if you have concerns. Otherwise, can you go ahead and create a git tag for v1.1.0?