More library functions (#51)

- units.parse, units.parse_bytes
- json.is_valid, json.marshal, json.unmarshal
- yaml.is_valid, yaml.marshal, yaml.unmarshal
- object.subset
- set_diff

* Also print number of errors due to each missing function
* Also lock down fully passing OPA suites

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

src/builtins/mod.rs

@@ -17,6 +17,7 @@ mod strings;
 mod time;
 mod tracing;
 pub mod types;
+mod units;
 mod utils;
 
 use crate::ast::{Expr, Ref};
@@ -65,7 +66,7 @@ lazy_static! {
 	//opa::register(&mut m);
 	debugging::register(&mut m);
 	tracing::register(&mut m);
-	
+	units::register(&mut m);
 	m
     };
 }