OPA conformance (#71)

- Remove unnecessary memory allocations
- Add --non-strict flag
- Ensure that only empty modules (ones without rules) are initialzed prior to evaluating rules.
- Record rule as entry for each of its prefixes.
  For example, for a rule a.b.c =... in package test, record it in
  rules["data.test.a"], rules["data.test.a.b"] and rules["data.test.a.b.c"]

  This allows evaluating the correct list of rules based on expessions
  a.b.c, a.b, a, data.test.a.b.c, data.test.a.b, data.test.a

Closes #69
Closes #70

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

src/utils.rs

@@ -86,17 +86,17 @@ pub fn get_path_string(refr: &Expr, document: Option<&str>) -> Result<String> {
     while expr.is_some() {
         match expr {
             Some(Expr::RefDot { refr, field, .. }) => {
-                comps.push(&field.text());
+                comps.push(field.text());
                 expr = Some(refr);
             }
             Some(Expr::RefBrack { refr, index, .. }) => {
                 if let Expr::String(s) = index.as_ref() {
-                    comps.push(&s.text());
+                    comps.push(s.text());
                 }
                 expr = Some(refr);
             }
             Some(Expr::Var(v)) => {
-                comps.push(&v.text());
+                comps.push(v.text());
                 expr = None;
             }
             _ => bail!("internal error: not a simple ref {expr:?}"),