add liquid comment syntax w/ tests

Includes single line comment syntax with # that ignores block wrap tag requirement (e.g. {% %} enclosing line comments) for functional usage.

tests/test_new.diff

@@ -435,3 +435,20 @@ index 0000000..2996176
 +	# TODO create the directory.
 +	$(AR) rc $@ $(OBJ)
 +
+diff --git a/tests/example_file.liquid b/tests/example_file.liquid
+new file mode 100644
+index 0000000..7cccc5b
+--- /dev/null
++++ b/tests/example_file.liquid
+@@ -0,0 +1,11 @@
++{% comment %} TODO: remove loop logic {% endcomment %}
++{% for i in (1..3) -%}
++ # TODO: Do math here!
++ # labels: help wanted
++  {{ i }}
++{% endfor %}
++{% comment %}
++TODO: Render Liquid file
++{% assign featured_product = all_products["product_handle"] %}
++{% render "product", product: featured_product %}
++{% endcomment %}