Comprehensive Rust v2 (#1073)

I've taken some work by @fw-immunant and others on the new organization
of the course and condensed it into a form amenable to a text editor and
some computational analysis. You can see the inputs in `course.py` but
the interesting bits are the output: `outline.md` and `slides.md`.

The idea is to break the course into more, smaller segments with
exercises at the ends and breaks in between. So `outline.md` lists the
segments, their duration, and sums those durations up per-day. It shows
we're about an hour too long right now! There are more details of the
segments in `slides.md`, or you can see mostly the same stuff in
`course.py`.

This now contains all of the content from the v1 course, ensuring both
that we've covered everything and that we'll have somewhere to redirect
every page.

Fixes #1082.
Fixes #1465.

---------

Co-authored-by: Nicole LeGare <dlegare.1001@gmail.com>
Co-authored-by: Martin Geisler <mgeisler@google.com>

src/modules/paths.md

@@ -1,4 +1,18 @@
-# Paths
+---
+minutes: 10
+---
+
+# use, super, self
+
+A module can bring symbols from another module into scope with `use`.
+You will typically see something like this at the top of each module:
+
+```rust,editable
+use std::collections::HashSet;
+use std::process::abort;
+```
+
+## Paths
 
 Paths are resolved as follows:
 
@@ -10,10 +24,29 @@ Paths are resolved as follows:
    * `crate::foo` refers to `foo` in the root of the current crate,
    * `bar::foo` refers to `foo` in the `bar` crate.
 
-A module can bring symbols from another module into scope with `use`.
-You will typically see something like this at the top of each module:
+<details>
 
-```rust,editable
-use std::collections::HashSet;
-use std::mem::transmute;
-```
+* It is common to "re-export" symbols at a shorter path. For example, the
+  top-level `lib.rs` in a crate might have
+
+  ```rust,ignore
+  mod storage;
+
+  pub use storage::disk::DiskStorage;
+  pub use storage::network::NetworkStorage;
+  ```
+
+  making `DiskStorage` and `NetworkStorage` available to other crates with a
+  convenient, short path.
+
+* For the most part, only items that appear in a module need to be `use`'d.
+  However, a trait must be in scope to call any methods on that trait, even if
+  a type implementing that trait is already in scope. For example, to use the
+  `read_to_string` method on a type implementing the `Read` trait, you need to
+  `use std::io::Read`.
+
+* The `use` statement can have a wildcard: `use std::io::*`. This is
+  discouraged because it is not clear which items are imported, and those might
+  change over time.
+
+</details>