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>

tests/opa.passing

@@ -50,6 +50,9 @@ intersection
 invalidkeyerror
 jsonfilter
 jsonfilteridempotent
+jsonremove
+jsonremoveidempotent
+jsonschema
 jwtencodesignheadererrors
 jwtencodesignpayloaderrors
 negation
@@ -96,5 +99,6 @@ typenamebuiltin
 undos
 union
 units
+uuid
 varreferences
 virtualdocs