C module loader and ffi native library loader

To test these loaders you need to manually copy `libs` directory in `koreader-base` made with `TARGET=android` to `/data/data/org.koreader.launcher/`in your Android device.

Note that these is also a shared library `libluajit.so` linked to each `libkoreader-*` module. The `libluajit.so` and the buildin `libluajit.a` should be the same version, otherwise the behavior of the application maybe undefined (may even restart your device), because we have got so much power now.