Add a new sub delimiter processor

Property definitions

markdown2 $ MdStaggeredDelimiterProcessor :: add
	# Add a new sub delimiter processor
	fun add(dp: MdDelimiterProcessor) do
		var len = dp.min_length
		var i = 0
		while i < processors.length do
			var p = processors[i]
			assert len != p.min_length else
				print "Cannot add two delimiter processor for `{delim}` " +
					"and mininimum length `{len}`"
			end
			if len > p.min_length then
				break
			end
			i += 1
		end
		processors.insert(dp, i)
	end
lib/markdown2/markdown_inline_parsing.nit:1261,2--1277,4