Add initial implementation of block tests

* Add blocktest cmd and support for block tests files in
  tests/BlockTests , the launched node does not connect to
  network, resets state with a genesis block from the test file
  and starts the RPC API

core/error.go

@@ -22,7 +22,7 @@ func (err *ParentErr) Error() string {
 }
 
 func ParentError(hash []byte) error {
-	return &ParentErr{Message: fmt.Sprintf("Block's parent unkown %x", hash)}
+	return &ParentErr{Message: fmt.Sprintf("Block's parent unknown %x", hash)}
 }
 
 func IsParentErr(err error) bool {