Why libsodium source is copied into this repository instead of ref linking with git submodules?

No complaints, just asking why libsodium original repository on github is not linked here as a submodule and instead the source files are manually duplicated in this repository. Not that there's anything wrong with it, it's just that a submodule linking might make it easier to manage the codebase. Otherwise, great work with PyNacl 👍🏼 