remove `extern crate core` and prelude imports

the latest Rust nightly makes this unnecessary

src/arch/common.rs

@@ -1,7 +1,6 @@
 // This file is part of libfringe, a low-level green threading library.
 // Copyright (c) 2015, edef <edef@edef.eu>
 // See the LICENSE file included in this distribution.
-use core::prelude::*;
 use core::mem::{size_of, align_of};
 use core::cmp::max;
 use core::ptr;

src/arch/mod.rs

@@ -1,7 +1,6 @@
 // This file is part of libfringe, a low-level green threading library.
 // Copyright (c) 2015, edef <edef@edef.eu>
 // See the LICENSE file included in this distribution.
-use core::prelude::*;
 pub use self::imp::Registers;
 
 unsafe impl Send for Registers {}

src/arch/x86_64/mod.rs

@@ -1,8 +1,6 @@
 // This file is part of libfringe, a low-level green threading library.
 // Copyright (c) 2015, edef <edef@edef.eu>
 // See the LICENSE file included in this distribution.
-use core::prelude::*;
-
 use stack::Stack;
 use super::common::{push, rust_trampoline};
 

src/context.rs

@@ -1,7 +1,6 @@
 // This file is part of libfringe, a low-level green threading library.
 // Copyright (c) 2015, edef <edef@edef.eu>
 // See the LICENSE file included in this distribution.
-use core::prelude::*;
 use core::marker::PhantomData;
 use arch::Registers;
 use stack;

src/debug/mod.rs

@@ -1,7 +1,6 @@
 // This file is part of libfringe, a low-level green threading library.
 // Copyright (c) 2015, edef <edef@edef.eu>
 // See the LICENSE file included in this distribution.
-use core::prelude::*;
 use stack;
 
 mod valgrind;

src/lib.rs

@@ -2,15 +2,12 @@
 // Copyright (c) 2015, edef <edef@edef.eu>
 // See the LICENSE file included in this distribution.
 #![feature(no_std)]
-#![feature(asm, core, core_prelude)]
+#![feature(asm, core)]
 #![no_std]
 
 //! libfringe is a low-level green threading library.
 //! It provides only a context-swapping mechanism.
 
-#[macro_use]
-extern crate core;
-
 #[cfg(test)]
 #[macro_use]
 extern crate std;

src/os/mod.rs

@@ -3,7 +3,6 @@
 // See the LICENSE file included in this distribution.
 
 extern crate std;
-use core::prelude::*;
 use self::std::io::Error as IoError;
 use stack;
 mod sys;

src/os/sys/unix.rs

@@ -2,7 +2,6 @@
 // Copyright (c) 2015, edef <edef@edef.eu>
 // See the LICENSE file included in this distribution.
 extern crate libc;
-use core::prelude::*;
 use self::libc::{c_void, c_int, size_t};
 use self::libc::{mmap, mprotect, munmap};
 use self::libc::MAP_FAILED;