use TARGET_ARCH instead of hardcoded arch in paths

use $(TARGET_ARCH) inside Android.mk to include prebuilts and includes depending on the target architecture.
Merge pull request #5 from ph0b/patch-1

use TARGET_ARCH instead of hardcoded arch in paths
remove "ref" as sodium.h has changed
Merge branch 'master' of https://github.com/joshjdevl/kalium-jni
update for latest libsodium remove "_ref"