strategy for built-in rules

[lzace817]

I suppose built-in rules should match with same semantic as user defined rules.
but there is no check for built-in corresponding to line 135.

built-in:

Noq/src/engine/rule.rs

Lines 155 to 157 in 716fae3

	if let Some(bindings) = Expr::replace_head().pattern_match(expr) {
	*match_count += 1;
	let meta_rule = Rule::User {

user:

Noq/src/engine/rule.rs

Lines 134 to 136 in 716fae3

	if let Some(bindings) = head.pattern_match(expr) {
	let resolution = strategy.matched(*match_count);
	*match_count += 1;

but I guess this feature is not released yet.

test case:

noq> test :: apply_rule(deep, b, c, apply_rule(deep, a, pair(b,b), a)) {