- Change group ID from com.ning to org.asynchttpclient.
- Update API packages:
   + com.ning --> org.asynchttpclient
   + compress package hierarchy to remove now redundant http.client sub-packages.

The package changes will occur over multiple commits to avoid a particularly annoying bug in Intellij as well as
git rebase -i change renamed files to rm/add thus losing all history.
- Update API packages (part 2):
   + com.ning --> org.asynchttpclient
   + compress package hierarchy to remove now redundant http.client sub-packages.
- Update API packages (part 3):
   + com.ning --> org.asynchttpclient
   + compress package hierarchy to remove now redundant http.client sub-packages.
- Update API packages (part 4):
   + com.ning --> org.asynchttpclient
   + compress package hierarchy to remove now redundant http.client sub-packages.
Final pass.  Fix remaining string references to com.ning.