loosen the lifetime bounds on Context

fix #6
ref #3

benches/context_new.rs

@@ -3,7 +3,7 @@ extern crate test;
 extern crate lwkt;
 use lwkt::{Context, Stack};
 
-static mut ctx_slot: *mut Context<SliceStack<'static>> = 0 as *mut Context<_>;
+static mut ctx_slot: *mut Context<'static, SliceStack<'static>> = 0 as *mut Context<_>;
 static mut stack_buf: [u8; 1024] = [0; 1024];
 
 #[bench]

benches/swap.rs

@@ -3,7 +3,7 @@ extern crate test;
 extern crate lwkt;
 use lwkt::{Context, StackSource};
 
-static mut ctx_slot: *mut Context<lwkt::os::Stack> = 0 as *mut Context<_>;
+static mut ctx_slot: *mut Context<'static, lwkt::os::Stack> = 0 as *mut Context<_>;
 
 #[bench]
 fn swap(b: &mut test::Bencher) {

examples/basic.rs

@@ -3,7 +3,7 @@ extern crate lwkt;
 use lwkt::{Context, StackSource};
 
 #[thread_local]
-static mut ctx_slot: *mut Context<lwkt::os::Stack> = 0 as *mut Context<_>;
+static mut ctx_slot: *mut Context<'static, lwkt::os::Stack> = 0 as *mut Context<_>;
 
 fn main() {
   unsafe {

src/context.rs

@@ -1,24 +1,27 @@
 use core::prelude::*;
+use core::marker::PhantomData;
 use arch::Registers;
 use stack;
 use debug::StackId;
 
-pub struct Context<Stack: stack::Stack> {
+pub struct Context<'a, Stack: stack::Stack> {
   regs: Registers,
   _stack_id: StackId,
-  stack: Stack
+  stack: Stack,
+  _ref: PhantomData<&'a ()>
 }
 
-impl<Stack> Context<Stack> where Stack: stack::Stack {
+impl<'a, Stack> Context<'a, Stack> where Stack: stack::Stack {
   #[inline]
-  pub unsafe fn new<F>(mut stack: Stack, f: F) -> Context<Stack>
+  pub unsafe fn new<F>(mut stack: Stack, f: F) -> Context<'a, Stack>
-    where F: FnOnce() + Send + 'static {
+    where F: FnOnce() + Send + 'a {
     let stack_id = StackId::register(&mut stack);
     let regs = Registers::new(&mut stack, f);
     Context {
       regs: regs,
       _stack_id: stack_id,
-      stack: stack
+      stack: stack,
+      _ref: PhantomData
     }
   }