Pasta Multi-Scalar Multiplication

This is an initial version with a list of planned improvements:

• parallelize;
• break down scalars to signed digits to half the buckets' integration complexity;
• switch to alternative bucket point representation with faster addition formula;
• migrate CUDA implementation;

To compile CUDA support ensure that you have nvcc, Nvidia CUDA compiler, on your program search path. Minimal installation suffices. For example on Ubuntu it would be sufficient to install cuda-minimal-build-11-7 instead of complete cuda package. If your laptop is equipped with a Turing+ controller, you're likely to have to compile with --features=cuda-mobile. Caveat lector. CUDA implementation does not adapt for the actual load yet, so that some results would be suboptimal.