Merge os, middle and meta subpackages

source/tanya/algorithm/iteration.d

@@ -20,10 +20,10 @@
  */
 module tanya.algorithm.iteration;
 
-import std.traits : Unqual, isMutable;
+import std.traits;
 import std.typecons;
 import tanya.memory.lifetime;
-import tanya.meta.trait;
+import tanya.meta;
 import tanya.range;
 
 private struct SingletonByValue(E)