Chapter 6 - Wrap all <Listing>s to comply with the virtual 80 chara…

…cter limit (READ DESC.)

I'm unsure whether wrapping the text may cause the listing text to be wrapped too as the newlines are found within quotation marks. If it causes issues, feel free to revert this commit. Another odd thing is that my editor uncolored the closing `</Listing>` tag when I split the lines. Maybe the newline characters need to be escaped with a backslash?

src/ch06-01-defining-an-enum.md

@@ -59,7 +59,8 @@ only know what *kind* it is. Given that you just learned about structs in
 Chapter 5, you might be tempted to tackle this problem with structs as shown in
 Listing 6-1.
 
-<Listing number="6-1" caption="Storing the data and `IpAddrKind` variant of an IP address using a `struct`">
+<Listing number="6-1" caption="Storing the data and `IpAddrKind` variant of an
+IP address using a `struct`">
 
 ```rust
 {{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-01/src/main.rs:here}}
@@ -141,7 +142,8 @@ more about bringing types into scope in Chapter 7.
 Let’s look at another example of an enum in Listing 6-2: this one has a wide
 variety of types embedded in its variants.
 
-<Listing number="6-2" caption="A `Message` enum whose variants each store different amounts and types of values">
+<Listing number="6-2" caption="A `Message` enum whose variants each store
+different amounts and types of values">
 
 ```rust
 {{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-02/src/main.rs:here}}

src/ch06-02-match.md

@@ -22,7 +22,8 @@ function that takes an unknown US coin and, in a similar way as the counting
 machine, determines which coin it is and returns its value in cents, as shown
 in Listing 6-3.
 
-<Listing number="6-3" caption="An enum and a `match` expression that has the variants of the enum as its patterns">
+<Listing number="6-3" caption="An enum and a `match` expression that has the
+variants of the enum as its patterns">
 
 ```rust
 {{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-03/src/main.rs:here}}
@@ -76,7 +77,8 @@ designs, so only quarters have this extra value. We can add this information to
 our `enum` by changing the `Quarter` variant to include a `UsState` value
 stored inside it, which we’ve done in Listing 6-4.
 
-<Listing number="6-4" caption="A `Coin` enum in which the `Quarter` variant also holds a `UsState` value">
+<Listing number="6-4" caption="A `Coin` enum in which the `Quarter` variant
+also holds a `UsState` value">
 
 ```rust
 {{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-04/src/main.rs:here}}
@@ -121,7 +123,8 @@ operations.
 This function is very easy to write, thanks to `match`, and will look like
 Listing 6-5.
 
-<Listing number="6-5" caption="A function that uses a `match` expression on an `Option<i32>`">
+<Listing number="6-5" caption="A function that uses a `match` expression on an
+`Option<i32>`">
 
 ```rust
 {{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-05/src/main.rs:here}}

src/ch06-03-if-let.md

@@ -6,7 +6,8 @@ program in Listing 6-6 that matches on an `Option<u8>` value in the
 `config_max` variable but only wants to execute code if the value is the `Some`
 variant.
 
-<Listing number="6-6" caption="A `match` that only cares about executing code when the value is `Some`">
+<Listing number="6-6" caption="A `match` that only cares about executing code
+when the value is `Some`">
 
 ```rust
 {{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-06/src/main.rs:here}}