Fix broken links using rustdoc nightly

Uses cross-crate documentation links so that rustdoc does the hard work
of making relative links for us.

Requires nightly version of rustdoc in order to generate links based on
path names, see
https://github.com/rust-lang/rfcs/blob/master/text/1946-intra-rustdoc-links.md
for details.

cranelift/wasm/src/module_translator.rs

@@ -10,7 +10,7 @@ use cranelift_codegen::timing;
 use wasmparser::{ModuleReader, SectionCode};
 
 /// Translate a sequence of bytes forming a valid Wasm binary into a list of valid Cranelift IR
-/// [`Function`](../codegen/ir/function/struct.Function.html).
+/// [`Function`](cranelift_codegen::ir::Function).
 pub fn translate_module<'data>(
     data: &'data [u8],
     environ: &mut dyn ModuleEnvironment<'data>,