Document some parameters to make Xamarin bindings happy
BingTileLayer: Move metadata retrrieval to an AsyncTask

This avoids avoid Strict Mode warnings in some cases.
Merge pull request #562 from kjeremy/async_bing_metadata

BingTileLayer: Move metadata retrrieval to an AsyncTask
Merge pull request #561 from kjeremy/javadoc_tweaks

Document some parameters to make Xamarin bindings happy
Merge remote-tracking branch 'upstream/mb-pages' into mb-pages