Move server and api into server pkg

This allows users to easily embed the
skydns server in their applications or allow
easier mocking in their tests.
Merge pull request #27 from crosbymichael/move-server

Move server and api into server pkg
Remove this unneeded comment
Update readme for * as wildcard
Remove 'any' and use '*' for the wildcard

The * is the actual wildcard that can be used in the DNS. Use
this.
Make external API also work with '*'
Update the test to work with * as the wildcard
typo in readme
Update README for callbacks

Some other minor types and added TODO item for patching
other things than only the TTL
First infrastructure for callbacks
Add Callback to Service

Some groundwork for callback, callback will be separately put in the
registry, but linked from each Service.
Extend the registry for callbacks

Add {Add,Remove}Callback to the registry so we can set these callbacks
Add AddCallbackCommand to command.go
Add callbacks to the services.
Put these CommandName functions on a single line
Add RemoveCallbackCommand
Make it compile again
Add seperate callback file
dont add it
Put the callbacks directly in the Service definition