Update README.txt instructions for android

Add clearer instructions for building android meterpreter.
Add android.release=true setting to android build.
Add link to android SDK URL.
Trailing slashes make maven sad.
Add instructions updating the Android SDK.
s/dalvikstager/ndkstager/g
deploy to data/android/libs
Merge remote-tracking branch 'origin'
update readme
add stage name placeholder and remove armeabi-v7a bin