tidy up htdb_record::unlink()
htdb_bench.cpp -> htdb_slab_bench.cpp
bugfix for slab_allocator when asserts are enabled.
fix asserts in slab_allocator::get()
add missing sync()s
makefile stuff
fix record_allocator::get() assert
+#define SLAB_DEBUG_ASSERTS
const correct methods.
sizes.hpp for calculating object sizes, file offsets .etc
updated blockchain.hpp
multimap_records - ht_records (hashtable records) + linked_records for single-key with multiple fixed size values.
will be used to implement history database.
replace deserializer with faster from_little_endian() in a few places.
message if read_htdb_record_value doesnt find value for key.
show_linked_records: add  linked_record_offset to record_size.
new tools: mmr_create, mmr_lookup, mmr_add_row, mmr_delete_last_row
htdb_record_bench
copied over tools/update_changelog.sh
leveldb_bench tool