spec loading cleanup (#858)

* spec loading cleanup in progress

* changed engine field in json spec

* refactored engine params

* polishing spec loading refactor

* fixed compiling json tests

* fixed compiling parity

* removed warnings

* removed commented out code

* fixed failing test

* bringing back removed TODO in spec.

json/src/uint.rs

@@ -23,7 +23,7 @@ use util::numbers::{U256, Uint as U};
 
 /// Lenient uint json deserialization for test json files.
 #[derive(Default, Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Copy)]
-pub struct Uint(U256);
+pub struct Uint(pub U256);
 
 impl Into<U256> for Uint {
 	fn into(self) -> U256 {
@@ -37,9 +37,15 @@ impl Into<u64> for Uint {
 	}
 }
 
+impl Into<usize> for Uint {
+	fn into(self) -> usize {
+		// TODO: clean it after util conversions refactored.
+		u64::from(self.0) as usize
+	}
+}
 impl Into<u8> for Uint {
 	fn into(self) -> u8 {
-		<Uint as Into<u64>>::into(self) as u8
+		u64::from(self.0) as u8
 	}
 }
 
@@ -55,6 +61,10 @@ struct UintVisitor;
 impl Visitor for UintVisitor {
 	type Value = Uint;
 
+	fn visit_u64<E>(&mut self, value: u64) -> Result<Self::Value, E> where E: Error {
+		Ok(Uint(U256::from(value)))
+	}
+
 	fn visit_str<E>(&mut self, value: &str) -> Result<Self::Value, E> where E: Error {
 		let value = match value.len() {
 			0 => U256::from(0),
@@ -83,12 +93,13 @@ mod test {
 
 	#[test]
 	fn uint_deserialization() {
-		let s = r#"["0xa", "10", "", "0x"]"#;
+		let s = r#"["0xa", "10", "", "0x", 0]"#;
 		let deserialized: Vec<Uint> = serde_json::from_str(s).unwrap();
 		assert_eq!(deserialized, vec![
 				   Uint(U256::from(10)),
 				   Uint(U256::from(10)),
 				   Uint(U256::from(0)),
+				   Uint(U256::from(0)),
 				   Uint(U256::from(0))
 		]);
 	}