only depend on windows deps on windows

[azdle]

As far as I can tell these are only used for windows. With these changes it still builds and works on linux for me. Not tested on any other platform.

[azdle]

That option doesn't work with the cargo that comes with 1.3.0 :/

Feel free to just close this if you're not okay with upping the required version of rust and I can just use a fork or something.

[newpavlov]

I think this should be merged and published. In ripgrep dependency graph as far as I can see only this crate and mmap do not use windows related crates as optional dependencies. (upd: oh, I see, this will be merged in 1.0)

P.S.: Also I think it's worth to add "requires Rust stable 1.8 or greater" to readme.

[BurntSushi]

@newpavlov Yes, this is a breaking change. I'll merge it when I'm ready to release the next semver incompatible release.

[newpavlov]

Small note: danburkert published memmap v0.5.0 with optional winapi dependencies. So it would be cool after publishing of the next walkdir release with this PR to update ripgrep dependencies too.

[BurntSushi]

OK, this is merged and now part of walkdir 1.0.0. Yay!

[BurntSushi]

@newpavlov Sadly, there's one dep remaining that needs to be updated, but it's out of my hands: ruuda/thread-id#3

[BurntSushi]

@newpavlov Even more sadly, the regex crate still supports Rust 1.3, so we can't actually make this work for ripgrep until the next semver bump of regex comes out, which should actually be pretty soon. Once that happens, then I think we are good to go.