added support for region parameters when geocoding address string

[androidseb]

I made these changes originally on the old repo:
https://github.com/devfd/react-native-geocoder
My app's code is using this old repo and I only needed iOS to work.
This part works for me, but please note that:
1/ For this repo, I have not tested the code at all, my changes worked on the old repo only for iOS
2/ I wrote the Android implementation the way I imagine it would work, hopefully it compiles

Feel free to use those changes or throw them away, I shared them in case it's useful...

[timwangdev]

Thanks, I will have a look next week.