Implement the native ad unit format to enable inline ads

[mannabri]

First of all, thanks for providing this plugin!

It would be great if I had the possibility to place ad units inline with app content. This would enable me to place ads in a scrollable content, e.g. a long article or a list of items.

Google AdMob provides the native ad format for this scenario:
https://support.google.com/admob/answer/7187428

[distante]

Please take a look at this #110.

I will pin it so It is easier to find.