Added a google_analytics field to BookConfig

This commit:
- Adds an Option<String> field to the BookConfig which should
  contain your google analytics ID
- Allows the google analytics ID to be extracted from the config
  file (key is google_analytics_id)
- Adds a test to make sure the field is populated from a config
  file correctly

src/book/bookconfig.rs

@@ -21,6 +21,7 @@ pub struct BookConfig {
 
     pub indent_spaces: i32,
     multilingual: bool,
+    pub google_analytics: Option<String>,
 }
 
 impl BookConfig {
@@ -37,6 +38,7 @@ impl BookConfig {
 
             indent_spaces: 4, // indentation used for SUMMARY.md
             multilingual: false,
+            google_analytics: None,
         }
     }
 
@@ -154,6 +156,11 @@ impl BookConfig {
             self.set_theme_path(&theme_path);
         }
 
+        // Google analytics code
+        if let Some(id) = config.get("google_analytics_id") {
+            self.google_analytics = Some(id.to_string().replace("\"", ""));
+        }
+
         self
     }
 

src/book/bookconfig_test.rs

@@ -347,3 +347,25 @@ fn it_parses_json_arrays_to_toml() {
 
     assert_eq!(format!("{:#?}", result), expected);
 }
+
+#[test]
+fn it_fetches_google_analytics_from_toml() {
+    let text = r#"
+title = "mdBook Documentation"
+description = "Create book from markdown files. Like Gitbook but implemented in Rust"
+author = "Mathieu David"
+google_analytics_id = "123456"
+"#;
+
+    let mut config = BookConfig::new(Path::new("."));
+
+    config.parse_from_toml_string(&text.to_string());
+
+    let mut expected = BookConfig::new(Path::new("."));
+    expected.title = "mdBook Documentation".to_string();
+    expected.author = "Mathieu David".to_string();
+    expected.description = "Create book from markdown files. Like Gitbook but implemented in Rust".to_string();
+    expected.google_analytics = Some("123456".to_string());
+
+    assert_eq!(format!("{:#?}", config), format!("{:#?}", expected));
+}