cuda: Add Windows Support

[matheusd]

This adds support to building the CUDA-enabled version of gominer on Windows, as well as adding instructions on how to do so.

Additionally, it switches from using a Makefile to using go generate in order to make the building process more idiomatic to Go projects.

[matheusd]

I wonder if the generate portion should just handle the building of the compiled blake3 cuda kernel and then a normal go build -tags cuda to actually build gominer after that?

Then we're back at having the user setup their own CGO_CFLAGS and CGO_LDFLAGS by hand, because those are also needed during the go build stage. Adding #cgo directives to the source code is not sufficient, because barnex/cuda5 requires cuda.h, and that isn't available by default on windows without setting up the env vars.

[davecgh]

Then we're back at having the user setup their own CGO_CFLAGS and CGO_LDFLAGS by hand, because those are also needed during the go build stage. Adding #cgo directives to the source code is not sufficient, because barnex/cuda5 requires cuda.h, and that isn't available by default on windows without setting up the env vars.

Ah, alright. I thought it was only needed for the nvcc bits to build the kernel.

[matheusd]

Updated readme with the various sections (view compiled file).

Also, I added a document which describes how to manually setup CUDA builds in windows (view)

[matheusd]

Made a first batch of review fixes.

[davecgh]

All of the updates thus far look good.

[matheusd]

Updated with changes to the debian section.

[davecgh]

I'll merge this after the squash.