* fix --help output in tests
* add tests to ensure we can use `purge.safelist`
* implement the `purge.safelist` for strings
* proxy `purge.safelist` to `purge.options.safelist`
This allows us to have a similar API in `AOT` and `JIT` mode.
* only proxy `purge.safelist` to `purge.options.safelist` if
`purge.options.safelist` doesn't exists yet.