Mas d31 i416 (#418)

* Add compression controls (#417)

* Add compression controls

Add configuration options to allow for a compression algorithm of `none` to disable compression altogether.  Also an option to change the point in the LSM tree when compression is applied.

* Handle configurable defaults consistently

Move them into leveled.hrl.  This forces double-definitions to be resolved.

There are some other constants in leveled_bookie that are relevant outside of leveled_bookie.  These are all now in the non-configurable startup defaults section.

* Clarify referred-to default is OTP not leveled

* Update leveled_bookie.erl

Handle xref issue with eunit include

src/leveled_codec.erl

@@ -106,7 +106,7 @@
 -type object_spec() ::
         object_spec_v0()|object_spec_v1().
 -type compression_method() ::
-        lz4|native.
+        lz4|native|none.
 -type index_specs() ::
         list({add|remove, any(), any()}).
 -type journal_keychanges() :: 
@@ -508,7 +508,9 @@ serialise_object(Object, true, Method) when is_binary(Object) ->
             {ok, Bin} = lz4:pack(Object),
             Bin;
         native ->
-            zlib:compress(Object)
+            zlib:compress(Object);
+        none ->
+            Object
     end;
 serialise_object(Object, false, _Method) ->
     term_to_binary(Object);
@@ -554,7 +556,8 @@ encode_valuetype(IsBinary, IsCompressed, Method) ->
     Bit3 = 
         case Method of 
             lz4 -> 4;
-            native -> 0
+            native -> 0;
+            none -> 0
         end,
     Bit2 =
         case IsBinary of            
@@ -562,7 +565,7 @@ encode_valuetype(IsBinary, IsCompressed, Method) ->
             false -> 0
         end,
     Bit1 =
-        case IsCompressed of
+        case IsCompressed and (Method =/= none) of
             true -> 1;
             false -> 0
         end,