Get the real language for src blocks from the org source.

default_environment/templates/html/src_block.dust

@@ -1,7 +1,6 @@
 <div class="src_block">
-  <!-- TODO: Get the language from the render context. -->
-  <div class="src_language">text</div>
-  <table class="src_body">
+  {?.language}<div class="src_language">{.language}</div>{/.language}
+    <table class="src_body">
     <tbody>
       {#.lines}
         <tr>

src/context/src_block.rs

@@ -11,10 +11,12 @@ use super::macros::render;
 #[serde(rename = "src_block")]
 pub(crate) struct RenderSrcBlock {
     lines: Vec<String>,
+    language: Option<String>,
 }
 
 render!(RenderSrcBlock, ISrcBlock, original, _render_context, {
     Ok(RenderSrcBlock {
         lines: original.lines.clone(),
+        language: original.language.clone(),
     })
 });

src/intermediate/src_block.rs

@@ -5,6 +5,7 @@ use crate::error::CustomError;
 #[derive(Debug, Clone)]
 pub(crate) struct ISrcBlock {
     pub(crate) lines: Vec<String>,
+    pub(crate) language: Option<String>,
 }
 
 intermediate!(
@@ -18,6 +19,7 @@ intermediate!(
             .split_inclusive('\n')
             .map(|s| s.to_owned())
             .collect();
-        Ok(ISrcBlock { lines })
+        let language = original.language.map(str::to_owned);
+        Ok(ISrcBlock { lines, language })
     }
 );