Expose size and memory used of a table

At the moment, the only way to do that via the API is to retrieve all
the entries and then call `length/1` or count the memory usage manually.
This should help speed things up when tables are particularly large.

src/rig.erl

@@ -10,6 +10,7 @@
 
 -export([
     all/1,
+    info/1,
     lock/1, lock_t/1,
     unlock/1, locks/0,
     read/2, read/3,
@@ -37,6 +38,16 @@ all(Table) ->
             {error, unknown_table}
     end.
 
+info(Table) ->
+    try
+        Tid = tid(Table),
+        Information = ets:info(Tid),
+        maps:with([memory, size], maps:from_list(Information))
+    catch
+        _:_ ->
+            {error, unknown_table}
+    end.
+
 % lock current version of the table
 -spec lock(table()) -> {ok, ets:tid()} | {error, Error :: _}.