Samples and Xamarin Component resources for xam generation.

Minor changes to the main Makefile so an alternate MDTOOL can be specified and
to avoid the clean target from failing.

Also, the component review guidelines prefer that the API revision 9 is targeted
for Android libraries and samples.
Knock down OkHttp's required SDK nonsense
Merge remote-tracking branch 'origin/pr/9'
Added the xamarin-component binary, to simplify setup.
Implement manual cancellation on Android
Close streams when we're done
Ignore build products
Add a playground project
Make sure we build our vendor DLL even in Release
Fix a crash where we'd end up doing network requests on the UI thread
More ConfigureAwait(false)s
Rewrite to handle returning headers early
Add an explicit cancel button to playground
Clean up code and add note about Mono bug
Add iOS Playground
Grumble
Abuse our existing stream wrapper some more
Fix multiple action wireups
Start to hack up AFNetworkingHandler to support early completion

EndOfStream is completely wrong and borked
Fix bugs, cancelation still mostly doesn't work :-/