A load of fiddling with Set, Vector and comparison operators

Signed-off-by: Rick Taylor <rick@tropicalstormsoftware.com>
Rejig Pair and add a load of explicit constructors

Signed-off-by: Rick Taylor <rick@tropicalstormsoftware.com>
Replace Table to match new Set implementation

Signed-off-by: Rick Taylor <rick@tropicalstormsoftware.com>
Add a load more operators to IteratorImpl

Signed-off-by: Rick Taylor <rick@tropicalstormsoftware.com>
Tidy up remove_at

Signed-off-by: Rick Taylor <rick@tropicalstormsoftware.com>
Tidy up Table and Set serach functions

Signed-off-by: Rick Taylor <rick@tropicalstormsoftware.com>
Add BTree - not working!

Signed-off-by: Rick Taylor <rick@tropicalstormsoftware.com>