tag-release: Shell script to simplify tagging releases.

It:
* sets the right `version` in Core.js and package.json,
* sets the right `build` in Core.js,
* commits these changes,
* tags the last commit with the given version,
* sets the new dev `version` in Core.js and package.json,
* reverts the `build` in Core.js,
* commits these changes.
Welcome 1.5.0.
Hello 1.5.1-dev.