Submodules for different gadgets & components about ethsnarks

[HarryR]

I think it could be split into the following sub-repos:

• ethsnarks-python - Python support
• ethsnarks-js - Javascript support (hopefully)
• ethsnarks-cxx - Gadgets and components in C++ for libsnark

Then the main ethsnarks repository combines them together, along with a libsnark distribution and build system, then ethsnarks-emscripten uses ethsnarks as a submodule to build it all for WebAssembly.

This would allow other projects to import only the functionality they need in the appropriate repository.

The ethsnarks repository would still have some C++ code where it combines the gadgets together.

My concerns are:

• the developer complexity of integration tests across multiple repositories
• building ethsnarks-cxx standalone, it wouldn't have libsnark as a submodule, and I don't think the CMake FindPKG would work well when it's a submodule of the ethsnarks project - or... work well at all for anybody. So it'd just have to be source code and some optional CMake files.