Added npm scripts for releasing new version

Related to issue #131 

This will allow you to release a new version by just calling `npm run release` (which defaults to `npm run release-patch`, you can also call `npm run release-minor` or `npm run release-major`). It updates package.json version, commits and pushes to master, makes the git tag, and publishes in npm. Should help for never forgetting to do all those steps when releasing. I use this script in Cycle too.

I guess you probably won't like the new "scripts" directory, but you can choose where and how to organize it. Anyway this whole PR is just a suggestion.