Add ability to control journal size by object count

This helps when there are files wiht large numbers of key deltas (and hence small values), where otherwise the object count may get out of control.

include/leveled.hrl

@@ -38,7 +38,8 @@
                         bloom :: binary() | none | undefined}).
 
 -record(cdb_options,
-                        {max_size :: integer() | undefined,
+                        {max_size :: pos_integer() | undefined,
+                        max_count :: pos_integer() | undefined,
                         file_path :: string() | undefined,
                         waste_path :: string() | undefined,
                         binary_mode = false :: boolean(),