General polish (#28)

Co-authored-by: Craig Everett <zxq9@zxq9.com>
Co-authored-by: Dimitar Ivanov <dimitar.p.ivanov@gmail.com>
Reviewed-on: #28

src/hz.erl

@@ -788,7 +788,7 @@ contract_code(ID) ->
          Result :: {ok,      Source}
                  | {project, Bundle}
                  | {error,   Reason},
-         Source :: string(),
+         Source :: binary(),
          Bundle :: [{FilePath :: string(), Contents :: binary()}],
          Reason :: chain_error() | string().
 %% @doc
@@ -809,6 +809,8 @@ extract(Blobby) ->
 
 extract2(TarBaby) ->
     case erl_tar:extract({binary, TarBaby}, [memory, compressed]) of
+        {ok, [{_File, Source}]} ->
+            {ok, Source};
         {ok, Bundle} ->
             {project, Bundle};
         Error ->
@@ -895,6 +897,11 @@ request(Path) ->
     hz_man:request(unicode:characters_to_list(Path)).
 
 
+-spec request(Path, Payload) -> {ok, Value} | {error, Reason}
+    when Path    :: unicode:charlist(),
+         Payload :: unicode:charlist(),
+         Value   :: map(),
+         Reason  :: hz:chain_error().
 request(Path, Payload) ->
     hz_man:request(unicode:characters_to_list(Path), Payload).
 
@@ -930,7 +937,7 @@ contract_create(CreatorID, Path, InitArgs) ->
             Gas = 500000,
             GasPrice = min_gas_price(),
             contract_create(CreatorID, Nonce,
-                            Amount, TTL, Gas, GasPrice,
+                            Gas, GasPrice, Amount, TTL,
                             Path, InitArgs);
         Error ->
             Error