Fix markdown warnings.

In current Rust, the usage of URLs like this result in warnings
when generating documentation.

src/encode.rs

@@ -32,7 +32,7 @@ enum Code {
 /// An Objective-C type encoding.
 ///
 /// For more information, see Apple's documentation:
-/// https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/ocrtTypeEncodings.html
+/// <https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/ocrtTypeEncodings.html>
 pub struct Encoding {
     code: Code,
 }

src/message/arm.rs

@@ -7,7 +7,7 @@ use super::Super;
 pub fn msg_send_fn<R: Any>(obj: *mut Object, _: Sel) -> (Imp, *mut Object) {
     // Double-word sized fundamental data types don't use stret,
     // but any composite type larger than 4 bytes does.
-    // http://infocenter.arm.com/help/topic/com.arm.doc.ihi0042e/IHI0042E_aapcs.pdf
+    // <http://infocenter.arm.com/help/topic/com.arm.doc.ihi0042e/IHI0042E_aapcs.pdf>
 
     extern {
         fn objc_msgSend();

src/message/arm64.rs

@@ -3,7 +3,7 @@ use super::Super;
 
 pub fn msg_send_fn<R>(obj: *mut Object, _: Sel) -> (Imp, *mut Object) {
     // stret is not even available in arm64.
-    // https://twitter.com/gparker/status/378079715824660480
+    // <https://twitter.com/gparker/status/378079715824660480>
 
     extern {
         fn objc_msgSend();

src/message/mod.rs

@@ -47,8 +47,8 @@ pub unsafe trait Message {
     Sends a message to self with the given selector and arguments.
 
     The correct version of `objc_msgSend` will be chosen based on the
-    return type. For more information, see Apple's documenation:
-    https://developer.apple.com/library/mac/documentation/Cocoa/Reference/ObjCRuntimeRef/index.html#//apple_ref/doc/uid/TP40001418-CH1g-88778
+    return type. For more information, see Apple's documentation:
+    <https://developer.apple.com/library/mac/documentation/Cocoa/Reference/ObjCRuntimeRef/index.html#//apple_ref/doc/uid/TP40001418-CH1g-88778>
 
     If the selector is known at compile-time, it is recommended to use the
     `msg_send!` macro rather than this method.

src/message/x86.rs

@@ -8,7 +8,7 @@ pub fn msg_send_fn<R: Any>(obj: *mut Object, _: Sel) -> (Imp, *mut Object) {
     // Structures 1 or 2 bytes in size are placed in EAX.
     // Structures 4 or 8 bytes in size are placed in: EAX and EDX.
     // Structures of other sizes are placed at the address supplied by the caller.
-    // https://developer.apple.com/library/mac/documentation/DeveloperTools/Conceptual/LowLevelABI/130-IA-32_Function_Calling_Conventions/IA32.html
+    // <https://developer.apple.com/library/mac/documentation/DeveloperTools/Conceptual/LowLevelABI/130-IA-32_Function_Calling_Conventions/IA32.html>
 
     extern {
         fn objc_msgSend();

src/message/x86_64.rs

@@ -7,7 +7,7 @@ pub fn msg_send_fn<R>(obj: *mut Object, _: Sel) -> (Imp, *mut Object) {
     // If the size of an object is larger than two eightbytes, it has class MEMORY.
     // If the type has class MEMORY, then the caller provides space for the return
     // value and passes the address of this storage.
-    // http://people.freebsd.org/~obrien/amd64-elf-abi.pdf
+    // <http://people.freebsd.org/~obrien/amd64-elf-abi.pdf>
 
     extern {
         fn objc_msgSend();

src/runtime.rs

@@ -1,7 +1,7 @@
 //! A Rust interface for the functionality of the Objective-C runtime.
 //!
 //! For more information on foreign functions, see Apple's documentation:
-//! https://developer.apple.com/library/mac/documentation/Cocoa/Reference/ObjCRuntimeRef/index.html
+//! <https://developer.apple.com/library/mac/documentation/Cocoa/Reference/ObjCRuntimeRef/index.html>
 
 use std::ffi::{CStr, CString};
 use std::fmt;