Redis 2.6 compat

Improves lzf decompression support to allow >2.6x compression ratio strings.
Adds https://github.com/JacobVorreuter/nsync/pull/5 rdb_load support.
Adds a test suite based on https://github.com/sripathikrishnan/redis-rdb-tools test vectors.

Still needs a bunch of work on ziplist/map parsing.