Using Rollup for building vue-highlighter

[Remeic]

Hi, we need to migrate to rollup instead of bili.
A good starting point: https://vuejs.org/v2/cookbook/packaging-sfc-for-npm.html
Instead of buble we want use babel ( latest version ) and serving all possible format.
Bundle size is a crucial part, so make attention to preset of babel. ( Advice use bugfixes
Minification must be delegated to the terser plugin.

Thanks in advance to all who will contribute to this Issue.
For any question, let we know

[khamer]

Just made the above PR (#28) for this. Because you're not using an SFC, it's a bit different than the cookbook but I just based it on how I've solved this before using rollup. Let me know if there's any feedback or issues.