Add auto release

This is a set of scripts that will automatically create a release whenever something is checked into master if the travis tests succeed.

It includes openpgp.min.js, openpgp-x.x.x.tgz and docs.zip in the release.

It also will update the docs into the gh-pages branch.

To enable it you need to:
1. Create a github token using the web page
2. Install the travis cli "npm install travis"
3. Add the encrypted token to .travis.yml "travis encrypt GITHUB_TOKEN=\<token from step1\>"
4. Update travis/success.sh to release docs to a different location if desired.