Merge pull request #35 from miekg/callback2

Implement the callback (as GET)
Cleanups
Documentation cleanups
doc tweak
Update the TODOs
Add callback test
Add tests
remove newline
Add tests
Add tests for the callbacks
remove debug
Add some logging
better test
Add TODO
Actuall perform the callbacks

Also fix adding them and check for an empty map.
dont run it in a go routine
fmt
Add service removal test for callback
Update comment
Implement the callback as an HTTP DELETE

Update the readme also.