Doc fix: list all module files Rust looks for.

1. In the English/Japanese phrases example in the "Multiple File
Crates" section of the "Crates and Modules" chapter, there are a total
of 8 module files that Rust looks for, while only four were
listed. This commit lists all 8 explicitly.
2. Title case fix.

Author: Varun Vats

src/doc/book/crates-and-modules.md

@@ -118,7 +118,7 @@ build  deps  examples  libphrases-a7448e02a0468eaa.rlib  native
 `libphrases-hash.rlib` is the compiled crate. Before we see how to use this
 crate from another crate, let’s break it up into multiple files.
 
-# Multiple file crates
+# Multiple File Crates
 
 If each crate were just one file, these files would get very large. It’s often
 easier to split up crates into multiple files, and Rust supports this in two
@@ -190,13 +190,19 @@ mod farewells;
 ```
 
 Again, these declarations tell Rust to look for either
-`src/english/greetings.rs` and `src/japanese/greetings.rs` or
-`src/english/farewells/mod.rs` and `src/japanese/farewells/mod.rs`. Because
-these sub-modules don’t have their own sub-modules, we’ve chosen to make them
-`src/english/greetings.rs` and `src/japanese/farewells.rs`. Whew!
-
-The contents of `src/english/greetings.rs` and `src/japanese/farewells.rs` are
-both empty at the moment. Let’s add some functions.
+`src/english/greetings.rs`, `src/english/farewells.rs`,
+`src/japanese/greetings.rs` and `src/japanese/farewells.rs` or
+`src/english/greetings/mod.rs`, `src/english/farewells/mod.rs`,
+`src/japanese/greetings/mod.rs` and
+`src/japanese/farewells/mod.rs`. Because these sub-modules don’t have
+their own sub-modules, we’ve chosen to make them
+`src/english/greetings.rs`, `src/english/farewells.rs`,
+`src/japanese/greetings.rs` and `src/japanese/farewells.rs`. Whew!
+
+The contents of `src/english/greetings.rs`,
+`src/english/farewells.rs`, `src/japanese/greetings.rs` and
+`src/japanese/farewells.rs` are all empty at the moment. Let’s add
+some functions.
 
 Put this in `src/english/greetings.rs`: