Enable leading whitespace stripping for blocks

tatsu_grammar.txt

@@ -55,7 +55,8 @@ block_end
 
 block_open
     =
-    @:"{%" {SP}*
+    | @:"{%" {SP}*
+    | {SP}* @:"{%-" {SP}*
     ;
 
 block_close

test_template.jinja

@@ -31,10 +31,10 @@ across lines #}
         The value will increase even more!
     {% endif %}
 {% endfor %}
-{% macro textarea(name, value='', rows=10, cols=40) -%}
+{%- macro textarea(name, value='', rows=10, cols=40) -%}
     <textarea name="{{ name }}" rows="{{ rows }}" cols="{{ cols
         }}">{{ value|e }}</textarea>
-{% endmacro -%}
+{%- endmacro -%}
 {# comment contents
 across lines #}
 <ul>