[x] Use ezgzip + ezjson and reimplement the compression later, if necessary.
[x] Drop LMDB and write something inspired by bap-cache, except that GC is done by fuzzy LRU (like relatime). Unfortunately we cannot use bap-cache directly because it will pull in a prohibitively large dependency tree.
[x] This library still intends to support using JSON everywhere.
New plan: drop camlzip and LMDB.