index: create kind+timestamp index database (William Casarin)

index: add u64_timestamp lmdb comparator (William Casarin)

debug: use mdb_strerror in more places (William Casarin)

filter: make sure we only match single chars (William Casarin)

pushed to nostrdb:refs/heads/master

http://git.jb55.com/nostrdb/commit/4b852f4362cfe7dd8b06cd9b6fbba4e11658ea32.html