Clarify documentation around module construction methods

[LukasPaczos]

We should clarify the inline docs and https://github.com/mapbox/mapbox-base-android/blob/master/MODULARIZATION.md to make it clear what types of approaches will the module loader attempt when creating the object without a custom configuration. This means clarifying that it's compatible with:

• class with a public, no-arg constructor
• Kotlin object
• Java-like singleton with a static