Complete support of maps in erl_syntax

	map_expr/1
	map_expr/2
	map_expr_argument/1
	map_expr_fields/1

	map_field_assoc/2
	map_field_assoc_name/1
	map_field_assoc_value/1

	map_field_exact/2
	map_field_exact_name/1
	map_field_exact_value/1