Add suport for line comments

This also switches comments to produce the same AST whether it is
an inline comment or a line comment.

tatsu_grammar.txt

@@ -17,6 +17,7 @@ expression
     | line_block_expression
     | variable_expression
     | comment_expression
+    | line_comment_expression
     ;
 
 raw_block_expression
@@ -229,7 +230,7 @@ filter_parameters
 
 comment_expression
     =
-    comment_open comment_content comment_close
+    comment_open comment:comment_content comment_close
     ;
 
 comment_open
@@ -247,6 +248,21 @@ comment_content
     { !comment_close CHAR }*
     ;
 
+line_comment_expression
+    =
+    line_comment_open comment:line_comment_content &"\n"
+    ;
+
+line_comment_open
+    =
+    "## "
+    ;
+
+line_comment_content
+    =
+    { !"\n" CHAR } *
+    ;
+
 content
     =
     !(
@@ -254,6 +270,7 @@ content
         | block_open
         | variable_open
         | comment_open
+        | line_comment_open
     ) CHAR ;
 
 LITERAL

test_template.jinja

@@ -35,9 +35,10 @@ across lines #}
     <textarea name="{{ name }}" rows="{{ rows }}" cols="{{ cols
         }}">{{ value|e }}</textarea>
 {% endmacro %}
+{# comment contents
+across lines #}
 <ul>
-# for href, caption in [('index.html', 'Index'),
-                        ('about.html', 'About')]:
-    <li><a href="{{ href }}">{{ caption }}</a></li>
+# for item in seq:
+    <li>{{ item }}</li>     ## this comment is ignored
 # endfor
 </ul>