Better separate modules

[marcellogalhardo]

Now that I have a better understanding on Compose implementation of ViewModels, to prepare for release 1.0.0 I propose a new module structure:

• core: vanilla functionalities. E.g., retain(viewModelStoreOwner, ...) {}.
• activity: activity extension functions, without Compose support. E.g., Activity.retain {}.
• activity-compose: activity extension functions, with Compose support. E.g., @Composable retainInActivity {}.
• fragment: fragment extension functions, without Compose support. E.g., Fragment.retain {}.
• fragment-compose: fragment extension functions, with Compose support. E.g., @Composable retainInFragment {}.
• navigation: navigation dedicated functionalities. E.g., retain(navBackStackEntry) {}.
• navigation-compose: navigation extension functions, with Compose support. E.g., @Composable retainInNavGraph {}.
• navigation-fragment: navigation extension functions, with Fragment support. E.g., Fragment.retainInNavGraph(navId) {}

This new structure will guarantee that new applications that only are built only with Compose do not require transitive dependency on fragments or other Android components.

[marcellogalhardo]

Fixed on #35.