Windows: use #![no_std]

[FaultyRAM]

I've rewritten the Windows version to use #![no_std], shaving off roughly 200 bytes.

Notes:

• #![no_std] executables are unstable, so this now requires nightly Rust for the time being.
• In line with the above, the Cargo dependencies on winapi and kernel32-sys had to be replaced with hand-written FFI bindings because they aren't #![no_std], which caused rustc to pull in a ton of dependencies and then fail to build the executable anyway. It might be worth investigating if the winapi crates can be #![no_std].
• /SUBSYSTEM:CONSOLE /NODEFAULTLIB now need to be passed to the linker. This removes dependencies on the CRT and other libraries that are normally linked in by default.