Remove the radix.Radix dependency

Put everything in maps. This removes to a major dependency and
makes Go DNS only depend on the core Go packages. This will
probably also be faster than the current setup -- although this
needs to be benchmarked.
Remove radix from core go dns
First pass at making zonedata more mem. efficient
More Zone api changes

Fix the tests for the new Zone api.
Update documentation
Fix signing

Fix the signing - the memory usage of the Zone structure is bad - and
needs to be fixed somehow.
Add some more tests
gofmt
Fix remove too
Fix remaining zone.Remove* functions

Fix the remove function and make them more like zone.Remove()
Update readme
In progress refactering of Remove*
Make removing work
Remove node locks
update documentation
Add nsec3 stuff
Update the Zone structure for NSEC and NSEC3
Add Sign3
Use Signature to be more in line with the non-plural RR
move functions closer together