N.B. This is work in progress, and doesn't actually work.

Append-only B+tree Erlang Term Storage (pure disk based)

abets is intended as a complement to dets, the standard Erlang term
disk storage utility. It aims to rectify some bad properties of dets;

1) no ordered set semantics
2) no graceful handling of force closed files
3) 2 GB limit per dets file
4) it's not disk-only (it will use some RAM)
5) dets has (as of 2010) at least one data-loss bug

This can be achieved by different trade-offs;

1) dets is normally faster
2) dets has less disk space overhead

Just like Erlang itself, abets will never modify data. But data can
become unreferenced, and subsequently garbage collected.

So, if data integrity, crash resiliency, +2GB tables or ordered set
semantics are more important than CPU time and disk space, abets will
be a win. Alas, dets also has the advantage of +10 year field testing,
while abets is partly vaporware.

abets is inspired by the eminent CouchDB (couchdb.apache.org), but
aims to be a more generic implementation of an Append-only B+tree data
structure.