Get rid of the tagged OID

This means we no longer accept any iolist in some of the functions,
but we might bring it back later.

There is also a new function, geef_ref:create_symbolic() to create
symbolic references, since we can no longer differentiate between a
name and an OID.

src/geef_oid.erl

@@ -7,21 +7,20 @@
 
 -include("geef_records.hrl").
 
--type oid() :: #geef_oid{oid :: binary()}.
+-type oid() :: <<_:160>>.
 -export_type([oid/0]).
 
 -export([parse/1, hex/1]).
 
 %% @doc Get a hex-encoded string of the hash
 -spec hex(geef_oid:oid()) -> binary().
-hex(#geef_oid{oid=Oid}) ->
+hex(Oid) ->
     geef_nif:oid_fmt(Oid).
 
 %% @doc Parse an iolist as a hash
--spec parse(iolist() | binary()) -> geef_oid:oid().
+-spec parse(iolist()) -> geef_oid:oid().
 parse(Sha) ->
-    Oid = geef_nif:oid_parse(Sha),
-    #geef_oid{oid=Oid}.
+    geef_nif:oid_parse(Sha).
 
 -ifdef(TEST).