Revert "Fix up links"

This reverts commit 7f1d1c6d9a7be5e427bace30e740b16b25f25c92.

The original commit was created because mdBook and rustdoc had
different generation algorithms for header links; now with
rust-lang/rust#39966 , the algorithms
are the same. So let's undo this change.

... when I came across this problem, I said "eh, this isn't fun,
but it doesn't take that long." I probably should have just actually
taken the time to fix upstream, given that they were amenable. Oh
well!

src/lib.rs

@@ -189,8 +189,8 @@
 //! [`sync`]: sync/index.html
 //! [`thread`]: thread/index.html
 //! [`use std::env`]: env/index.html
-//! [`use`]: ../book/crates-and-modules.html#Importing%20Modules%20with%20use
-//! [crate root]: ../book/crates-and-modules.html#Basic%20terminology%3A%20Crates%20and%20Modules
+//! [`use`]: ../book/crates-and-modules.html#importing-modules-with-use
+//! [crate root]: ../book/crates-and-modules.html#basic-terminology-crates-and-modules
 //! [crates.io]: https://crates.io
 //! [deref coercions]: ../book/deref-coercions.html
 //! [files]: fs/struct.File.html

src/primitive_docs.rs

@@ -490,7 +490,7 @@ mod prim_str { }
 /// assert_eq!(tuple.2, 'c');
 /// ```
 ///
-/// For more about tuples, see [the book](../book/primitive-types.html#Tuples).
+/// For more about tuples, see [the book](../book/primitive-types.html#tuples).
 ///
 /// # Trait implementations
 ///