Improve no_std support, update for latest nightly

Cargo.toml

 [package]
 name = "orbclient"
-version = "0.3.20"
+version = "0.3.21"
 authors = ["Jeremy Soller <jackpot51@gmail.com>"]
 description = "The Orbital Client Library"
 documentation = "https://docs.rs/orbclient"
@@ -20,7 +20,7 @@ no_std = []
 [lib]
 name = "orbclient"
 path = "src/lib.rs"
-[target.'cfg(all(not(feature="no_std"), not(target_os="redox")))'.dependencies]
+[target.'cfg(all(not(feature="no_std"), any(unix, windows)))'.dependencies]
 sdl2 = "0.31.0"
 [target.'cfg(all(not(feature="no_std"), target_os="redox"))'.dependencies]
 redox_syscall = "0.1.43"

LICENSE

 The MIT License (MIT)
 
-Copyright (c) 2015 Jeremy Soller
+Copyright (c) 2015-2019 Jeremy Soller
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -19,4 +19,3 @@ AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
-

src/lib.rs

@@ -46,6 +46,6 @@ pub enum Mode {
 #[path = "sys/orbital.rs"]
 mod sys;
 
-#[cfg(all(not(feature = "no_std"), not(target_os = "redox")))]
+#[cfg(all(not(feature = "no_std"), any(unix, windows)))]
 #[path = "sys/sdl2.rs"]
 mod sys;

src/sys/sdl2.rs

 extern crate sdl2;
 
 use std::cell::Cell;
-use std::sync::atomic::{AtomicUsize, Ordering, ATOMIC_USIZE_INIT};
+use std::sync::atomic::{AtomicUsize, Ordering};
 use std::{mem, ptr, slice};
 
 use color::Color;
@@ -10,7 +10,7 @@ use renderer::Renderer;
 use Mode;
 use WindowFlag;
 
-static SDL_USAGES: AtomicUsize = ATOMIC_USIZE_INIT;
+static SDL_USAGES: AtomicUsize = AtomicUsize::new(0);
 /// SDL2 Context
 static mut SDL_CTX: *mut sdl2::Sdl = ptr::null_mut();
 /// Video Context