templates evaluate at global scope, breaks statement`return;`

Return statements can only be added inside a function but templates are evaluated by babel at the global scope so babel throws on

```
statement`return;`
```

Example: http://felix-kling.de/esprima_ast_explorer/#/1lLYuPcGmT

This also happens for `break;` statements as well.

@fkling had an idea of always evaluating templates within a function but that could break things like `import` that can only be added at the global scope. Not sure what the way forward is here but i find the templating extremely valuable so it would be great to find a solution!