The `is` keyword, for is annotations

Property definitions

	# The `is` keyword, for *is* annotations
	var n_kwis: nullable TKwis = null is writable

src/parser/parser_nodes.nit:3058,2--3059,46

	redef fun n_kwis=(node)
	do
		_n_kwis = node
		if node != null then node.parent = self
	end

src/parser/parser_prod.nit:8661,2--8665,4