Update the treebuf test to use the generic library
Fix Atter, stop Nexter using At(elem)
Implement At() on Atter

This allows to resume search from already existing Atter.
Update the tests.

Use generic.Collection as a collection handle.

Introduce a new test for the upcoming Mknode from Atter
Update the nexter to the generic.Value api
Introduce the new MkNode method from an atter.
Implement Atter.MkNode() operator

Use the operator in a test case.
Use the colmgr.Root key in the trunk node.
Update the nexter's At method signature

We must use colmgr.Atter
Update the test for Nexter

To test freezing using At() and continuing using Next()
Currently it doesn't work well
Add NexterAtter as a paused nexter.
A working NexterAtter freezing and resuming of Nexter
Move the MkNode to the mknode file.

Introduce a new test for an Atter.At() bug,
where the new atter is incorrectly at the root.
The tree is rooted at root.trunk.l instead of root.trunk.r

This simplifies the insertion algorithms.
The tree in testcase 3 of wrong Atter.MkNode is now broken

We fix this using an upcoming left gap and right gap
The at() bug seems to be fixed.
Nexters now freeze using At() when updating or viewing a node
Append to an empty collection works fine
Drop Map and Upd from Nexter.
The Atter can now be Fix()-ed