fs

Re-published from [futures-fs](https://github.com/seanmonstar/futures-fs), access File System operations off-thread, using Futures and Streams.

Usage

let fs = FsPool::default();

// our source file
let read = fs.read("/home/sean/foo.txt", Default::default());

// default writes options to create a new file
let write = fs.write("/home/sean/out.txt", Default::default());

// block this thread!
// the reading and writing however will happen off-thread
read.forward(write).wait()
    .expect("IO error piping foo.txt to out.txt");