Don't require the static runtime for openblas on Windows

[ethanhs]

As part of shipping openblas-src on Windows as part of a Python package, I would like to link dynamically to the CRT (this greatly reduces binary size). Currently I cannot do so because openblas-src forces linking to a static CRT.

I have made this patch as a workaround. I could also add a feature flag that only on Windows sets the static CRT if you would prefer, otherwise it can be left up to the parent crate what to do in a build.rs.

[termoshtt]

I would like to link dynamically to the CRT (this greatly reduces binary size)

It is reasonable. As vcpkg-rs's document says, we have three options and should add one more option for windows-x64-static-md case.

I prefer to add new flag crt-static, which will be ignored when static=false:

	static=true	static=false (default)
crt-static=true	x64-windows-static	x64-windows
crt-static=false (default)	x64-windows-static-md	x64-windows

[termoshtt]

I prefer to add new flag crt-static, which will be ignored when static=false:

https://doc.rust-lang.org/reference/linkage.html#static-and-dynamic-c-runtimes

RUSTFLAGS='-C target-feature=+crt-static' cargo build --target x86_64-pc-windows-msvc

Looking the reference, there is an example to specify +crt-static in RUSTFLAG for just this case. This must be preferable instead of introducing crt-static flag, which requires me to add new flag to upstream crate e.g. ndarray-linalg.

[termoshtt]

Merged through #71 with CI and README update