Core tracedb functionality. (#996)

* fixed encoding 0u8

* simplified if else stmt

* tracedb core

* more comprehensive tracedb tests

* fixed minor review issues

* addresses filter

* fixed typos

* replace malformed with corrupted

* trace switch

* db key is generic and can be made smaller

* smaller tracedb keys

* tracedb version

* fixed ignored tests

* rename Tracedb -> TraceDB

* fixed typos

* proves

* trace only top level calls to builtins to avoid DDoS attacks

* fixed tracedb config switches

* fix comments fat replaced with trace

* vector-addressing scheme for localized traces

* removed comments

* removed first, redundant 0 from trace address

* updated db.trace method

* additional tests for tracedb.trace()

util/src/hash.rs

@@ -78,6 +78,12 @@ macro_rules! impl_hash {
 		/// Unformatted binary data of fixed length.
 		pub struct $from (pub [u8; $size]);
 
+		impl From<[u8; $size]> for $from {
+			fn from(bytes: [u8; $size]) -> Self {
+				$from(bytes)
+			}
+		}
+
 		impl Deref for $from {
 			type Target = [u8];
 

util/src/rlp/rlperrors.rs

@@ -40,7 +40,9 @@ pub enum DecoderError {
 	/// Non-canonical (longer than necessary) representation used for data or list.
 	RlpInvalidIndirection,
 	/// Declared length is inconsistent with data specified after.
-	RlpInconsistentLengthAndData
+	RlpInconsistentLengthAndData,
+	/// Custom rlp decoding error.
+	Custom(&'static str),
 }
 
 impl StdError for DecoderError {