Like write_to but take care of creating the file

Property definitions

core :: file $ Writable :: write_to_file
	# Like `write_to` but take care of creating the file
	fun write_to_file(filepath: String)
	do
		var stream = new FileWriter.open(filepath)
		write_to(stream)
		stream.close
	end
lib/core/file.nit:366,2--372,4