Add documentation
Atoms in the TLB must be unique.

There must not be duplicates; in particular, atoms not in an atomtable
cannot have a Handle.
Get rid of unused HashCode

Dead code clutters and make things complex. Lets keep things simple.
The atom handle already provides a unique ID.  If you want to use it
as a hash, then knock out a few low-order bits.
Use C++11 unordered_map instead of boost.
Remove more unused hash codes.
Remove another user of HandleEntry
Kill another HandleEntry user.
Remove the last user of HandleEntry
Get rid of HandleEntry completely.
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