Add x86_64-pc-windows-msvc and i686-pc-windows-msvc configurations

[briansmith]

Unfortunately, crypto-bench doesn't build on pc-windows-msvc now because several of the libraries fail to build. As Cargo.toml only supports adding dependencies per-target, not removing them, that means we'd need to add an exhaustive set of configurations to Cargo.toml in order to get this to work. Hopefully the instead the libraries will soon improve so that they build and work correctly on pc-windows-msvc.

[briansmith]

Also, when this is done, an Appveyor CI config should be checked in, and Brian should update his Appveyor config to enable it for this repo.

[briansmith]

@ctz has made some progress on rust-fastpbkdf2 at ctz/rust-fastpbkdf2#1.
rust-crypto now builds and works on -msvc, after DaGenix/rust-crypto#324.
I am probably going to change rust-openssl to be Linux- (and maybe Mac-) only, to work around the difficulty in getting it working when OpenSSL isn't already installed as a system library.

[briansmith]

After 8a073da, we can now use cargo_all bench to run whichever benchmarks actually work on Windows. The Appveyor configuration is still pending.

[briansmith]

I'm closing this. I run crypto-bench on ring on -msvc regularly lately. I'll file a separate issue for Appveyor.