create a manual garbage collection utility

Project:M36 currently uses a very simple Binary dump to store each transaction. However, if each commit grows the database, we can see O(n^2) growth in overall database size. As a short-term counter-measure, we could implement a garbage collection utility which would take an existing database and trim it to only its latest transactions, deleting all history before that.

Another possible way to reduce database size would be to implement some compression scheme.