dojo/_base/lang API doc cleanup:

   1. Document module exports rather than dojo globals, ie: lang.extend(), not dojo.extend().
   2. Inline methods into export hash, rather than using intermediate local variables.
   3. Replace dependency on dojo/_base/sniff with dependency on slimmer (and non-deprecated) dojo/sniff.
   
 Refs #13101 !strict.

git-svn-id: http://svn.dojotoolkit.org/src/dojo/trunk@28602 560b804f-0ae3-0310-86f3-f6aa0a117693