change attribute doc links

to point to the "Reexports" section. The older links don't work correctly on
docs.rs. The "Reexports" section always has valid links to the documentation of
each attribute.

Author: japaric

cortex-m-rt/src/lib.rs

@@ -16,19 +16,18 @@
 //!
 //! This crate also provides the following attributes:
 //!
-//! - [`#[entry]`] to declare the entry point of the program
-//! - [`#[exception]`] to override an exception handler. If not overridden all exception handlers
+//! - `#[entry]` to declare the entry point of the program
+//! - `#[exception]` to override an exception handler. If not overridden all exception handlers
 //!   default to an infinite loop.
-//! - [`#[pre_init]`] to run code *before* `static` variables are initialized
-//!
-//! [`#[entry]`]: ../cortex_m_rt_macros/fn.entry.html
-//! [`#[exception]`]: ../cortex_m_rt_macros/fn.exception.html
-//! [`#[pre_init]`]: ../cortex_m_rt_macros/fn.pre_init.html
+//!   default to an infinite loop.
+//! - `#[pre_init]` to run code *before* `static` variables are initialized
 //!
 //! This crate also implements a related attribute called `#[interrupt]`, which allows you
 //! to define interrupt handlers. However, since which interrupts are available depends on the
 //! microcontroller in use, this attribute should be re-exported and used from a device crate.
 //!
+//! The documentation for these attributes can be found in the [Reexports](#reexports) section.
+//!
 //! # Requirements
 //!
 //! ## `memory.x`