Top-down evaluation (#177)

When executing a query, only those rules that are used
by the query will be evaluated.

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

examples/regorus.rs

@@ -72,6 +72,7 @@ fn rego_eval(
 
     // Evaluate query.
     let results = engine.eval_query(query, enable_tracing)?;
+
     println!("{}", serde_json::to_string_pretty(&results)?);
 
     #[cfg(feature = "coverage")]
@@ -147,11 +148,11 @@ enum RegorusCommand {
         #[arg(long, short)]
         trace: bool,
 
-        // Non strict execution
+        /// Perform non-strict evaluation. (default behavior of OPA).
         #[arg(long, short)]
         non_strict: bool,
 
-        // Display coverage information
+        /// Display coverage information
         #[cfg(feature = "coverage")]
         #[arg(long, short)]
         coverage: bool,