Purge oldest guild posts beyond the limit (100 messages, 4 news) after
each new post is created. Replace misleading alliance application TODO
with a note that the feature is not yet implemented.
Fix unchecked error returns on bf.Seek(), db.Exec(), QueryRow().Scan(),
pkt.Build(), logger.Sync(), and binary.Write() calls. The linter now
passes with 0 errors, build compiles, and all tests pass with -race.