Merge os, middle and meta subpackages

source/tanya/range/adapter.d

@@ -14,10 +14,10 @@
  */
 module tanya.range.adapter;
 
-import std.traits : hasMember, isArray;
+import std.traits;
 import tanya.algorithm.mutation;
 import tanya.memory.lifetime;
-import tanya.meta.trait;
+import tanya.meta;
 import tanya.range;
 
 private mixin template InserterCtor()

source/tanya/range/primitive.d

@@ -15,9 +15,9 @@
 module tanya.range.primitive;
 
 import std.algorithm.comparison;
-import std.traits : FunctionAttribute, ReturnType, hasElaborateCopyConstructor, functionAttributes;
+import std.traits;
 import tanya.memory.lifetime;
-import tanya.meta.trait;
+import tanya.meta;
 import tanya.range.array;
 
 /**