add theme option (#95)

closes #89

src/main.rs

@@ -223,7 +223,7 @@ fn run() -> Result<()> {
             let config = app.config()?;
 
             let assets = HighlightingAssets::new();
-            let theme = assets.default_theme()?;
+            let theme = assets.get_theme(config.theme.unwrap_or("Default"))?;
 
             if app.matches.is_present("list-languages") {
                 let languages = assets.syntax_set.syntaxes();
@@ -269,6 +269,14 @@ fn run() -> Result<()> {
                 return Ok(());
             }
 
+            if app.matches.is_present("list-themes") {
+                let themes = &assets.theme_set.themes;
+                for (theme, _) in themes.iter() {
+                    println!("{}", theme);
+                }
+                return Ok(());
+            }
+
             let mut output_type = get_output_type(config.paging);
             let handle = output_type.handle()?;
             let mut printer = Printer::new(handle, &config);