Add cryptopp as a submodule

[patstew]

There's a comment in the readme about not being able to add this as a submodule to cryptopp, but why not do it the other way around? It makes it easier to use, e.g. as a submodule in other projects. It also means that each commit in this repo is tied to a specific commit in cryptopp that it can build correctly, so when files are moved around it doesn't cause problems.

[janisozaur]

I assume the problems mentioned are not regarding adding submodule itself, but rather having the files from submodule in the top-level directory. A way around that could be having cryptopp-cmake as a submodule, but then using symlinks in the top level directory.

cryptopp
├─ cryptopp-cmake # a submodule
└─ CMakeLists.txt -> cryptopp-cmake/CMakeLists.txt

[Vollstrecker]

I'm still working on the other way around. So you can just checkout the source in the top-level dir, or with starting cmake 3.11, let this be done within the configure-step itself.

[abdes]

Please check the latest version. We now support many different ways to auto-fetch crypto++ without the additional maintenance overhead of crypto++ as a sub-module.

git submodules require things to be done to keep them up-to-date and consistent which are error-prone.