auto merge of #11364 : brson/rust/docs, r=alexcrichton

This reorganizes the documentation index to be more focused on the in-tree docs, and to clean up the style, and it also adds @steveklabnik's pointer guide.

Author: bors

configure

@@ -801,7 +801,8 @@ do
     make_dir $h/test/doc-tutorial
     make_dir $h/test/doc-guide-ffi
     make_dir $h/test/doc-guide-macros
-    make_dir $h/test/doc-guide-borrowed-ptr
+    make_dir $h/test/doc-guide-lifetimes
+    make_dir $h/test/doc-guide-pointers
     make_dir $h/test/doc-guide-container
     make_dir $h/test/doc-guide-tasks
     make_dir $h/test/doc-guide-conditions