Cursors: Just use normal Int64s instead of Halfdecent.Numerics
Collections: Index ordered collections by Int64 instead of IInteger

64 bit integers are big enough for any collection and are easier to program.
Collections.Tests: Use == instead of .Equals() for Int64 indexes
Collections: Initial tree functionality

- A basic node type
- Traversal events (for any kind of node)
- Recursive depth-first traversal algorithm (for any kind of node)
- Tests