Diff null sources

[hedgar2017]

Resolves the issue

[dariusc93]

What you should do to reduce repeated code is to put

#[cfg(target_os = "windows")]
const NULL_SOURCE: &str = "nul";
#[cfg(target_os = "linux")]
const NULL_SOURCE: &str = "/dev/null";

in text/mod.rs then do use crate::bindings::text::NULL_SOURCE in any code, or maybe put them in one of the crates this crate uses (eg patch?) and include it. Same with PR #258 and maybe #255 ?

[hedgar2017]

Merged with PR #258