Release script

[RishabhKarnad]

The release script does the following:

• asks for new version number
• bumps package versions to the specified version
• creates a build
• creates a release commit
• runs np to create the release tag and publish vue-native-core
• publishes vue-native-helper, vue-native-scripts and vue-native-template-compiler with npm publish

If np fails, then the release commit is reset and the script exits.

No tests or linting written yet, so np uses the --yolo flag. This will be removed later.