Scope annotations must have Runtime Retention

[dlemures]

Scope annotations defined by the user must have Runtime Retention (same as @singleton does).
Otherwise, the runtime checks won't work for those annotation.

Should we force it?
Crash the compiler if any does not have the right retention.

[stephanenicolas]

I think it would be a good practice to enforce. Though there is an issue with annotation with runtime retention : all classes using the annotation will be kept in first dex...

[stephanenicolas]

We should just fail, the first dex would not be impacted much.

[dlemures]

We will fail at compile time if it does not contain the right retention.

[dlemures]

PR: #191

[dlemures]

WIKI updated: https://github.com/stephanenicolas/toothpick/wiki/Scope-Annotations#custom-scope-annotations

[dlemures]

PR merged.