* split flatbuffers.h into separate files
* wrong variable in cmakelists for android
* readded two accidentally deleted includes
* created buffer.h and moved buffer related things over
Android build was dated, using the Android.mk approach. Current
project configuration on Android encourages the usage of CMake, so we
are updating the android project as an example on how to use either the
Java/Kotlin generate code or the native C++ one.